I am trying to fetch a simple JSON element from express.js. I am trying have React assign it to a state variable on the front end. I am using this code to do so:
componentDidMount() {
fetch("/user")
.then(response => response.json())
.then(result => this.setState({myUser:result}))
}
But when I run typeof myUser after this setState command, it says string instead of object. I've tried using JSON.parse(), etc. But either I get an error or it continues to assign the data as a string rather than JSON. What sort of syntax do I need to use in this fetch-then context to coerce the data assignment to be JSON?
I have read this link:
With this code:
componentDidMount(){
fetch('https://abx.com/data/tool.json').then(response =>{
if (!response.ok) throw Error('Response not ok')
return response.json(); // This is built in JSON.parse wrapped as a Promise
}).then(json => {
this.setState({"sections" : json});
}).catch(err =>{
console.log(err);
});
}
But it doesn't solve the problem. I ran this code directly in my application verbatim. When I run typeof on the variable, it says string instead of object. I looked at other posts on Stack Overflow, but I did not see a solution to this.
I figured out what was going wrong (after many hours of experimenting):
On the server side, I was creating a "homegrown" JSON object using string and variable concatenation. I also tried creating the JSON object by doing this:
var str = "name:" + name + ", department:" + department
var user = {str};
Both of these were not working in subtle ways... despite trying different types of gadgetry on the client side, I couldn't get React to interpret the data as a JSON object. But then I had an idea to construct the JSON on the server side (in Express.js) like this:
var user = {};
user["name"] = name;
user["department"] = department;
That immediately cleared things up on the server side and the client side. When using setState() in React, it now sets the value as an object (which was the goal all along).
I think this can be useful to others... if React doesn't seem to understand the JSON, perhaps it is being sent from the server in a subtly incorrect format.
Related
I am writing a private plugin for nodebb (open forum software). In the nodebb's webserver.js file there is a line that seems to be hogging all incoming json data.
app.use(bodyParser.json(jsonOpts));
I am trying to convert all incoming json data for one of my end-points into raw data. However the challenge is I cannot remove or modify the line above.
The following code works ONLY if I temporarily remove the line above.
var rawBodySaver = function (req, res, buf, encoding) {
if (buf && buf.length) {
req.rawBody = buf.toString(encoding || 'utf8');
}
}
app.use(bodyParser.json({ verify: rawBodySaver }));
However as soon as I put the app.use(bodyParser.json(jsonOpts)); middleware back into the webserver.js file it stops working. So it seems like body-parser only processes the first parser that matches the incoming data type and then skips all the rest?
How can I get around that? I could not find any information in their official documentation.
Any help is greatly appreciated.
** Update **
The problem I am trying to solve is to correctly handle an incoming stripe webhook event. In the official stripe documentation they suggested I do the following:
// Match the raw body to content type application/json
app.post('/webhook', bodyParser.raw({type: 'application/json'}),
(request, response) => {
const sig = request.headers['stripe-signature'];
let event;
try {
event = stripe.webhooks.constructEvent(request.body, sig,
endpointSecret);
} catch (err) {
return response.status(400).send(Webhook Error:
${err.message});
}
Both methods, the original at the top of this post and the official stripe recommended way, construct the stripe event correctly but only if I remove the middleware in webserver. So my understanding now is that you cannot have multiple middleware to handle the same incoming data. I don't have much wiggle room when it comes to the first middleware except for being able to modify the argument (jsonOpts) that is being passed to it and comes from a .json file. I tried adding a verify field but I couldn't figure out how to add a function as its value. I hope this makes sense and sorry for not stating what problem I am trying to solve initially.
The only solution I can find without modifying the NodeBB code is to insert your middleware in a convenient hook (that will be later than you want) and then hack into the layer list in the app router to move that middleware earlier in the app layer list to get it in front of the things you want to be in front of.
This is a hack so if Express changes their internal implementation at some future time, then this could break. But, if they ever changed this part of the implementation, it would likely only be in a major revision (as in Express 4 ==> Express 5) and you could just adapt the code to fit the new scheme or perhaps NodeBB will have given you an appropriate hook by then.
The basic concept is as follows:
Get the router you need to modify. It appears it's the app router you want for NodeBB.
Insert your middleware/route as you normally would to allow Express to do all the normal setup for your middleware/route and insert it in the internal Layer list in the app router.
Then, reach into the list, take it off the end of the list (where it was just added) and insert it earlier in the list.
Figure out where to put it earlier in the list. You probably don't want it at the very start of the list because that would put it after some helpful system middleware that makes things like query parameter parsing work. So, the code looks for the first middleware that has a name we don't recognize from the built-in names we know and insert it right after that.
Here's the code for a function to insert your middleware.
function getAppRouter(app) {
// History:
// Express 4.x throws when accessing app.router and the router is on app._router
// But, the router is lazy initialized with app.lazyrouter()
// Express 5.x again supports app.router
// And, it handles the lazy construction of the router for you
let router;
try {
router = app.router; // Works for Express 5.x, Express 4.x will throw when accessing
} catch(e) {}
if (!router) {
// Express 4.x
if (typeof app.lazyrouter === "function") {
// make sure router has been created
app.lazyrouter();
}
router = app._router;
}
if (!router) {
throw new Error("Couldn't find app router");
}
return router;
}
// insert a method on the app router near the front of the list
function insertAppMethod(app, method, path, fn) {
let router = getAppRouter(app);
let stack = router.stack;
// allow function to be called with no path
// as insertAppMethod(app, metod, fn);
if (typeof path === "function") {
fn = path;
path = null;
}
// add the handler to the end of the list
if (path) {
app[method](path, fn);
} else {
app[method](fn);
}
// now remove it from the stack
let layerObj = stack.pop();
// now insert it near the front of the stack,
// but after a couple pre-built middleware's installed by Express itself
let skips = new Set(["query", "expressInit"]);
for (let i = 0; i < stack.length; i++) {
if (!skips.has(stack[i].name)) {
// insert it here before this item
stack.splice(i, 0, layerObj);
break;
}
}
}
You would then use this to insert your method like this from any NodeBB hook that provides you the app object sometime during startup. It will create your /webhook route handler and then insert it earlier in the layer list (before the other body-parser middleware).
let rawMiddleware = bodyParser.raw({type: 'application/json'});
insertAppMethod(app, 'post', '/webhook', (request, response, next) => {
rawMiddleware(request, response, (err) => {
if (err) {
next(err);
return;
}
const sig = request.headers['stripe-signature'];
let event;
try {
event = stripe.webhooks.constructEvent(request.body, sig, endpointSecret);
// you need to either call next() or send a response here
} catch (err) {
return response.status(400).send(`Webhook Error: ${err.message}`);
}
});
});
The bodyParser.json() middleware does the following:
Check the response type of an incoming request to see if it is application/json.
If it is that type, then read the body from the incoming stream to get all the data from the stream.
When it has all the data from the stream, parse it as JSON and put the result into req.body so follow-on request handlers can access the already-read and already-parsed data there.
Because it reads the data from the stream, there is no longer any more data in the stream. Unless it saves the raw data somewhere (I haven't looked to see if it does), then the original RAW data is gone - it's been read from the stream already. This is why you can't have multiple different middleware all trying to process the same request body. Whichever one goes first reads the data from the incoming stream and then the original data is no longer there in the stream.
To help you find a solution, we need to know what end-problem you're really trying to solve? You will not be able to have two middlewares both looking for the same content-type and both reading the request body. You could replace bodyParser.json() that does both what it does now and does something else for your purpose in the same middleware, but not in separate middleware.
I got my json file and I am getting it on the service. Then I am trying to subscribe to it in the component, but in console.log(this.jsonObj) I get empty array. Also if I write console.log(data) - I get json data.
Service :
objUrl = 'assets/jsons/obs.json';
constructor(private http: HttpClient) {
console.log('Hello ObjectsProvider Provider');
}
getObjectsJson() {
return this.http.get(this.objUrl);
}
Component :
jsonObj = {};
this.object.getObjectsJson().subscribe((data =>
this.jsonObj = data
))
console.log(this.jsonObj)
Issue
You are trying to get the Asynchronous data in Synchronous fashion. You are logging the data console.log(this.jsonObj) outside of Observable. So it will get executed without waiting for the result to come from API.
Fix
Just move the log or any code you want to execute the after API inside subscribe. So you your code will look like
jsonObj = [];
this.object.getObjectsJson().subscribe((data =>
this.jsonObj = data;
console.log(this.jsonObj); //<-- data will be appear here.
))
The service method is asynchronous, so the code inside the subscribe() (which makes the assignment) executes at some time in the future, when the http call returns. Your log statement is outside of the subscription, so it happens before the assignment. Try putting the log statement inside the subscription, right after the assignment.
console.log(this.jsonObj) will run before the response of the server. You can work with it as it is. It will run perfectly. you can test it like this
<p *ngIf="jsonObj !== undefined">{{jsonObj.field}}</p>
if you want to check it with console.log, just add it in the subscription like this
this.http.getObjectsJson().subscribe((data => {
this.jsonObj = data
console.log(this.jsonObj)
}));"
The Aurelia fetch client docs have a basic example of getting json data:
bind() {
let client = new HttpClient();
return client.fetch('data.json')
.then(response => response.json())
.then(data => {
console.log(data[1]);
});
}
The above works fine yet the following does not:
files = [];
bind() {
let client = new HttpClient();
return client.fetch('data.json')
.then(response => response.json())
.then(files => this.files = files);
}
Gulp now complains "error TS2322: Type 'Response' is not assignable to type 'any[]'."
Even more odd is that I now get XHR 404 errors in my console. This makes no sense; the data.json file had no issue being found and fetched the first time. The only difference in the second code snippet is that instead of logging the data to the console, I'm actually trying to do something with it.
I believe your specific issue may be caused by an older version of TypeScript (2.1, the latest is 2.5). If you have an opportunity to do so, you can try updating it.
response in the statement response => is of type Response defined by Aurelia. When you are running this.files = files, it seems like TypeScript thinks that files is of type Response. You are already implicitly declaring this.files as type any[], so the assignment is not allowed.
You can get around this by setting an explicit type for files, or even just using any:
.then((files: any[]) => this.files = files);
I would try to avoid using any to get around type safety and work with the types, but the issue you're running into appears to be a bug in the version of TypeScript and/or Aurelia that you're using.
I'm using Angular 4 to develop an app which is mainly about displaying data from DB and CRUD.
Long story short I found that in Angular 4 the component html doesn't like displaying loosely typed object (leaving the space blank while displaying other things like normal with no warning or error given in console) even if it can be easily displayed in console.log output, as shown in a string.
So I made a function in the service file to cast the values into a set structure indicating they're strings.
So now something like this works:
HTML
...
<div>{{something.value}}</div>
...
Component.ts
...
ngOnInit() {
this.route.params.subscribe(params => {
this.pkey = params['pkey'];
this.service.getSomethingById(this.pkey)
.then(
something => {
this.something = this.service.convertToStructure(something);
},
error => this.errorMessage = <any>error);
});
}
...
Code of the function convertToStructure(something)
convertToStructure(someArr: myStructure): myStructure {
let something: myStructure = new myStructure();
something.value = someArr[0].value;
return something;
}
But as I dig into other files for copy and paste and learn skills from what my partner worked (we're both new to Angular) I found that he did NOT cast the said values into a fixed structure.
He thought my problem on not being able to display the values (before I solved the problem) was because of me not realizing it was not a plain JSON object {...} but an array with a single element containing the object [{...}] .
He only solved half of my problem, cause adding [0] in html/component.ts was not able to make it work.
Component.ts when it did NOT work
...
ngOnInit() {
this.route.params.subscribe(params => {
this.pkey = params['pkey'];
this.service.getSomethingById(this.pkey)
.then(
something => {
console.log(something[0].value); //"the value"
this.something = something[0]; //html can't find its value
},
error => this.errorMessage = <any>error);
});
}
...
HTML when it did NOT work
...
<div>{{something[0].value}}</div> <!--Gives error on the debug console saying can't find 'value' of undefined-->
...
And of course when I'm using the failed HTML I only used this.something = something instead of putting in the [0], and vice versa.
So I looked into his code in some other page that display similar data, and I found that he used *ngFor in html to extract the data and what surprised me is that his html WORKED even if both of our original data from the promise is identical (using the same service to get the same object from sever).
Here's what he did in html:
...
<div *ngFor="let obj of objArr" ... >
{{obj.value}}
</div>
...
His html worked.
I'm not sure what happened, both of us are using a raw response from the same service promise but using for loop in html makes it automatically treat the value as strings while me trying to simply inject the value fails even if console.log shows a double quoted string.
What's the difference between having the for loop and not having any for loop but injecting the variable into html directly?
Why didn't he have to tell Angular to use the set structure indicating the values are strings while me having to do all the trouble to let html knows it's but a string?
The difference here is as you said that your JSON is not simple object , its JSON Array and to display data from JSON array you need loop. So, that is why your friends code worked and yours did not. And please also add JSON as well.
This is a slightly messy questions. Although it appears I'm asking question about amCharts, I really just trying to figure how to extract an array from HTTP request and then turn it into a variable and place it in to 3-party javacript.
It all starts here, with this question, which was kindly answered by AmCharts support.
As one can see from the plnker. The chart is working. Data for the chart is hard coded:
`var chartData = [{date: new Date(2015,2,31,0,0,0, 0),value:372.10,volume:2506100},{date: new Date(2015,3,1,0, 0, 0, 0),value:370.26,volume:2458100},{date: new Date(2015,3,2,0, 0, 0, 0),value:372.25,volume:1875300},{date: new Date(2015,3,6,0, 0, 0, 0),value:377.04,volume:3050700}];`
So we know the amCharts part works. Know where the problem is changing hard coded data to a json request so it can be dynamic. I don't think this should be tremendously difficult, but for the life of me I can't seem figure it out.
The first issue is I can't find any documentation on .map, .subscribe, or .observable.
So here is a plunker that looks very similar to the first one, however it has an http providers and injectable. It's broken, because I can't figure out how to pull the data from the service an place it into the AmCharts function. I know how pull data from a http provider and display it in template using NgFor, but I don't need it in the template (view). As you can see, I'm successful in transferring the data from the service, with the getTitle() function.
this.chart_data =_dataService.getEntries();
console.log('Does this work? '+this.chart_data);
this.title = _dataService.getTitle();
console.log('This works '+this.title);
// Transfer the http request to chartData to it can go into Amcharts
// I think this should be string?
var chartData = this.chart_data;
So the ultimate question is why can't I use a service to get data, turn that data into a variable and place it into a chart. I suspect a few clues might be in options.json as the json might not be formatted correctly? Am I declaring the correct variables? Finally, it might have something to do with observable / map?
You have a few things here. First this is a class, keep it that way. By that I mean to move the functions you have inside your constructor out of it and make them methods of your class.
Second, you have this piece of code
this.chart_data =_dataService.getEntries().subscribe((data) => {
this.chart_data = data;
});
What happens inside subscribe runs asynchronously therefore this.chart_data won't exist out of it. What you're doing here is assigning the object itself, in this case what subscribe returns, not the http response. So you can simply put your library initialization inside of the subscribe and that'll work.
_dataService.getEntries().subscribe((data) => {
if (AmCharts.isReady) {
this.createStockChart(data);
} else {
AmCharts.ready(() => this.createStockChart(data));
}
});
Now, finally you have an interesting thing. In your JSON you have your date properties contain a string with new Date inside, that's nothing but a string and your library requires (for what I tested) a Date object, so you need to parse it. The problem here is that you can't parse nor stringify by default a Date object. We need to convert that string to a Date object.
Look at this snippet code, I used eval (PLEASE DON'T DO IT YOURSELF, IS JUST FOR SHOWING PURPOSES!)
let chartData = [];
for(let i = 0; i < data[0].chart_data.length; i++) {
chartData.push({
// FOR SHOWING PURPOSES ONLY, DON'T TRY IT AT HOME
// This will parse the string to an actual Date object
date : eval(data[0].chart_data[i].date);
value : data[0].chart_data[i].value;
volume : data[0].chart_data[i].volume;
});
}
Here what I'm doing is reconstructing the array so the values are as required.
For the latter case you'll have to construct your json using (new Date('YOUR DATE')).toJSON() and you can parse it to a Date object using new Date(yourJSON) (referece Date.prototype.toJSON() - MDN). This is something you should resolve in your server side. Assuming you already solved that, your code should look as follows
// The date property in your json file should be stringified using new Date(...).toJSON()
date : new Date(data[0].chart_data[i].date);
Here's a plnkr with the evil eval. Remember, you have to send the date as a JSON from the server to your client and in your client you have to parse it to a Date.
I hope this helps you a little bit.
If the getEntries method of DataService returns an observable, you need to subscribe on it to get data:
_dataService.getEntries().subscribe(
(data) => {
this.chart_data = data;
});
Don't forget that data are received asynchronously from an HTTP call. The http.get method returns an observable (something "similar" to promise) will receive the data in the future. But when the getEntries method returns the data aren't there yet...
The getTitle is a synchronous method so you can call it the way you did.