We Keep Coding

Loading images in vue.js from an API

Consider this:
An API loads a manifest of image metadata. The images have an ID, and with another API call returns a base64 image from the DB. The model for the manifest is attachmentRecord and the ID is simply a field.
I would rather not preload these large strings into an array (that would work).
so I have this (which lazy loads on any manifest change):
<div v-for="(attachment, index) in attachmentRecord" :key="index">
<img :src="fetchImage(attachment.id)" />
</div>
fetchimage() is a wrapper for an axios function which returns back from a promise. (writing this from memory):
this.axios({
method: "get",
url: url,
}).then(res => res.data)
.catch(() => {
alert("Unable to load raw attachment from this task and ID");
});
}
Now, the network calls go thru fine, the ID passes in correctly, I can see the base 64data, but they don't seem to make it to wrapper function or the src attribute. It always comes up blank. I tried wrapping it in another promise,only to get a promise back to the src attribute. What would be a best practice for this situation in Vue?
Ok, so far I made these changes with Constantin's help:
I tried to strip it down without a helper function:
Vue template Code:
<div v-for="(attachment, index) in attachmentRecord" :key="index">
<img :src="getAttachmentFromTask(attachment.id)" />
base method:
async getAttachmentFromTask(attachmentID) {
if (!attachmentID) alert("Unknown Attachment!");
let sendBack = "";
let url = "/server/..."
await this.axios({
method: "get",
url: url
})
.then(res => {
sendBack = res.data;
})
.catch(() => {
alert("Unable to load raw attachment from this task and ID");
});
// >>>>>>>>>alerts base64 correctly; Vue loads [object Promise] in img
alert(sendBack);
return sendBack;
}

It turns out that Vue doesn't handle async / await as well as I thought. Therefore, you have to save the image data to each attachment in attachmentRecord. This getAttachmentFromTask method now handles this when accessed the first time and populates a data property for the corresponding attachment object. On successive calls, that property is returned if it is already populated. Note the usage of Vue.set() because the property is not available in the initial data, but we want it to be reactive. You can even set up a fallback image like a loader, see the shortly flickering SO logo without text before the larger logo appears:
new Vue({
el: '#app',
data: {
attachmentRecord: [{
id: 1
}]
},
methods: {
getAttachmentFromTask(attachmentIndex, attachmentID) {
let record = this.attachmentRecord[attachmentIndex];
if (!record.data) {
Vue.set(record, 'data', null);
axios.get('https://kunden.48design.de/stackoverflow/image-base64-api-mockup.json').then((result) => {
Vue.set(record, 'data', result.data);
});
}
return this.attachmentRecord[attachmentIndex].data;
}
}
});
img {
max-width: 100vw;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/axios/0.19.0/axios.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.6.10/vue.min.js"></script>
<div id="app">
<div v-for="(attachment, index) in attachmentRecord" :key="index">
<img :src="getAttachmentFromTask(index, attachment.id) || 'https://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-icon.png'" />
</div>
</div>
old answer: (Unfortunately doesn't work that way with Vue currently)
Axios requests are asynchronous by default. So the function doesn't wait for then() to return the value. You could add the async keyword before your fetchImage function name and add the await keyword before this.axios. Then make the then callback assign the return value to a variable in the fetchImage function scope and have the function return it.
async fetchImage() {
let returnValue;
await this.axios({
method: "get",
url: url,
}).then(res => { returnValue = res.data; })
.catch(() => {
alert("Unable to load raw attachment from this task and ID");
});
return returnValue;
}

Async Computed in Components - VueJS?

I'm finding a solution to async computed method in Components:
Currently, my component is:
<div class="msg_content">
{{messages}}
</div>
<script>
export default {
computed: {
messages: {
get () {
return api.get(`/users/${this.value.username}/message/`, {'headers': { 'Authorization': 'JWT ...' }})
.then(response => response.data)
}
}
},
}
</script>
Result:
{}
How to rewrite it in Promise mode? Because I think we can async computed by writing into Promise mode.

Computed properties are basically functions that cache their results so that they don't have to be calculated every time they are needed. They updated automatically based on the reactive values they use.
Your computed does not use any reactive items, so there's no point in its being a computed. It returns a Promise now (assuming the usual behavior of then).
It's not entirely clear what you want to achieve, but my best guess is that you should create a data item to hold response.data, and make your api.get call in the created hook. Something like
export default {
data() {
return {
//...
messages: []
};
},
created() {
api.get(`/users/${this.value.username}/message/`, {
'headers': {
'Authorization': 'JWT ...'
}
})
.then(response => this.messages = response.data);
}
}

es7 makes doing this quite trivial by using async and await in conjunction with axios' returned promise. You'll need the vue-async-computed package.
export default {
asyncComputed: {
async myResolvedValue() {
return await api.get(`/users/${this.value.username}/message/`, {'headers': { 'Authorization': 'JWT ...' }})
.then(response => response.data)
}
}
}

I bumped on a similar case where I need to re-run the computed function to fetch from a server every time a data or a props changes.
Without installing any extra package (vue-async-computed or vue3-async-computed as pointed by other answers), you can force a data to reload by creating a "virtual" computed method.
Lets say you want to fetch data from the server every time the user types their username, and depending on what was typed, you want to show a given message from the server.
From the example below, username and messages in this case are both reactive data, but there is no direct connection between them, so lets create a computed that depends on username by returning its value, which will force it to be called every time username is changed. Now you just need to call a function that can be async and will update messages after fetching from the server.
In the example below, I use ":dummy" just to force a call to my computed function.
<template>
<input v-model="username">
<div class="msg_content" :dummy="force_react">
{{messages}}
</div>
</template>
<script>
export default {
data: function () {
return {
messages: "",
username: "",
};
},
computed: {
force_react: function() {
this.get(); // called every time that this.username updates
return this.username; // becase its result depends on username
}
},
methods: {
async get() { // get's called every time that this.username updates
console.log("Got called");
let response = await api.get(`/users/${this.username}/message/`, {'headers': { 'Authorization': 'JWT ...' }});
this.messages = response.data;
}
},
}
</script>
You can see a working example here in Vue SFC playground

Why not using a watcher? Vue Documentation
You can use async function in the callback of the watcher.

Method not working from created hook Vue.js

I am trying to create a web app based on a database. Setup: NodeJS and a Vuejs 2 app generated with the CLI (with Webpack). Currently, I am using axios to retrieve records into an object. Based on that object I want to draw some svg lines from certain points to other points. The method works completely as designed when running it from an #click (v-on directive). However, when I try to add it to the created hook it doesn't work. No errors displayed. It's just not running. Does anyone no why? Code example below.
<template>
<div class="holder">
<step v-for="item in steps"></step>
<events v-for="point in points"></events>
<button #click= "createArrows">Test</button>
</div>
</template>
<script>
import axios from 'axios'
import Step from './Step.vue'
import Events from './Events.vue'
export default {
name: 'Graph',
data () {
return {
steps: '',
events: '',
points: []
},
components: {
Step, Events
},
methods: {
getSteps: function() {
let getsteps = this
axios.get('localhost:8000/api/steps')
.then(function (response) {
getsteps.steps = response.data
})
.catch(function (error) {
getsteps.steps = "Invalid request"
})
},
getEvents: function() {
let getevents = this
axios.get('localhost:8000/api/events')
.then(function (response) {
getevents.events = response.data
})
.catch(function (error) {
getevents.events = "Invalid request"
})
},
createArrows: function() {
},
created() {
this.getSteps(),
this.getEvents(),
this.createArrows()
}
}
EDIT: Promises are already included in the axios library. Since I am new to this concept I missed this one. Refactored code below:
methods: {
getData: function() {
let getdata = this
axios.all([
axios.get('localhost:8000/api/steps'),
axios.get('localhost:8000/api/events')
])
.then(axios.spread(function (stepResponse, eventResponse) {
console.log('success')
getdata.steps = stepResponse.data
getdata.events = eventResponse.data
getdata.createArrows()
}))
.catch(function (error) {
console.log("Invalid request")
})
},
createArrows: function() {
}
},
created() {
this.getData()
}
}
</script>

I think it's a classic async issue.
With v-on, your call to createArrows is "timewise after" getSteps and getEvents: meaning that getSteps and getEvents have finished executing their internal ajax promises, have populated the relevant data into the component instance for createArrows to find and access.
However, inside the created() hook, if you think about it, the calls fall through to createArrows() instantaneously (before the promisy things inside getSteps and getEvents have finished).
You'll have to refactor the call to createArrows inside created() as promise resolve for it work there correctly.

React Component JSON Callback Scope

I'm using generator-react-webpack to create a React web app. This web app relies on JSON feeds - one of which is hosted on a CDN that does not support JSONP and the CDN url is a subdomain of the webapp. Is there any way to return the JSON data from within the React Component?
Basic React Component:
var AppComponent = React.createClass({
loadData: function() {
jQuery.getJSON(jsonFile.json?callback=?)
.done(function(data) {
console.log(data);
}.bind(this));
},
render: function(){
return ( ... );
}
});
I've tried a few solutions, and have come to the conclusion that I need to define my own callback on the JSON file like so:
JSON:
handleData({
"data": "hello World"
})
Is there a way for the handleData callback to be defined in the react component, or the response accessed from the react component? Any thoughts as to how I can get this to work are much appreciated. Thanks!

This looks like an odd way to do things, especially the part where you're using jQuery. That's a client-side utility to overcome not knowing where everything is and not having direct access to your elements. It makes no sense to use it when you're using React weith Webpack for bundling: React already knows where everything is (using refs) and Webpack means you can just use regular universal Node modules for everything that you need to do.
I'd recommend using something like, using request or a similar universal fetch API:
// loadData.js
var request = require('request');
var loadData = function(urlYouNeed, handler) {
request(urlYouNeed, function(error, response, body) {
if (error) {
return handler(error, false);
}
// do anything processing you need on the body,
var data = process(body);
handler(false, data);
};
So: just a module you can require in any component you define with require('./loadData'). And then in your actual component you do this:
var loadData = require('./loadData');
var AppComponent = React.createClass({
getDefaultProps: function() {
return {
jsonURL: "cdn://whateverjson.json"
};
},
getInitialState: function() {
loadData(this.props.jsonURL, this.updateData);
return {
data: []
}
},
updateData: function(err, data) {
if (err) {
return console.error(err);
}
data = secondaryEnsureRightFormat(data);
this.setState({ data: data });
},
render: function(){
var actualThings = this.state.data.map((entry, pos) => {
return <Whatever content={entry} key={entry.dontUseThePosVariableUpThere}/>
});
return (
<div>
...
{actualThings}
...
</div>
);
}
});
Much cleaner.

If I understand correctly the question, you only have to change your loadData this way :
loadData: function() {
var c = this
jQuery.getJSON(jsonFile.json?callback=?)
.done(function(data) {
c.handleData(data)
});
},
handleData: function(data) {
/* Implement here the function to handle the data */
},

Isomorphic React.js & iso-http

I'm building a react web application which I'd like to render both server side and client side. I've been working off isomorphic-react-template but I've used iso-http to make a query to my content server. My aim is to have the app when server-side query the content server directly and render the content to HTML; and to have the app when client-side to do a normal AJAX request for content.
Here's the code I'm using. It works great on the browser, but the server-side render doesn't include the data; I presume because the server-side render isn't waiting for the async http call to return before it compiles the HTML and sends it over:
componentDidMount: function() {
var id = this.getParams().id;
var classThis = this;
request
.get("http://content.example.com/things/" + id)
.end(function(response) {
response.body = JSON.parse(response.text);
if (response.ok) {
classThis.setState({ data: response.body });
} else {
classThis.setState({ data: null });
}
});
}
I know this is all fairly new stuff; but is there a known way to solve this problem, so that the server side renderer waits for certain async calls to complete before sending?

I've managed to get this working with react-async.
I've pulled out my async function like this so I can call it from componentDidMount and from the asynchronous getInitialStateAsync function that ReactAsync uses:
mixins: [ ReactAsync.Mixin ],
getInitialStateAsync: function(callback) {
this.getContent(function(state) {
callback(null, state)
}.bind(this))
},
componentDidMount: function() {
this.getContent(function(state) {
this.setState(state);
}.bind(this));
},
getContent: function(callback) {
var id = this.getParams().id;
request
.get("http://content.example.com/things/" + id)
.end(function(response) {
response.body = JSON.parse(response.text);
if (response.ok) {
callback({ error: {}, post: response.body })
} else {
callback({ post: {}, error: response.body });
}
});
}
Then in my server.jsx I'm rendering with the async functions:
ReactAsync.renderToStringAsync(<Handler />, function(err, markup) {
var html = React.renderToStaticMarkup(<Html title={title} markup={markup} />);
res.send('<!DOCTYPE html>' + html);
});
Obviously there is huge potential for cock up here (the whole page fails to render if the server isn't present) but this feels like the start of the right approach!