Why is lodash not working when I import it in Vue.js - vue.js

Question

I created a fresh new install of vue.js using "vue create todo --default" command. After that I installed lodash too with this command "npm i --save lodash". I can see it in my package.json on the "dependencies" object. The problem is that when I import it on my main.js and use the lodash functions, it is showing the error "_ is not defined". So I tried importing it inside the App.vue. The error "_ is not defined" was removed but it is not working.
Here are the code inside the App.vue, main.js, and package.json
main.js
import Vue from 'vue'
import App from './App.vue'
import "bootstrap/dist/css/bootstrap.min.css";
import "jquery/dist/jquery";
import "bootstrap/dist/js/bootstrap.min";
import _ from "lodash";
Vue.prototype._ = _;
Vue.config.productionTip = false
new Vue({
render: h => h(App),
}).$mount('#app')
App.vue
<template>
<div id="app">
<h4 class="bg-primary text-white text-center p-2">
{{name}}'s' To Do List
</h4>
<div class="container-fluid p-4">
<div class="row">
<div class="col font-weight-bold">Task</div>
<div class="col-2 font-weight-bold">Done</div>
</div>
<div class="row" v-for="t in completedtask" v-bind:key="t.action">
<div class="col">{{t.action}}</div>
<div class="col-2">
<input type="checkbox" v-model="t.done" class="form-check-input">
{{t.done}}
</div>
</div>
</div>
</div>
</template>
<script>
export default {
data(){
return{
name: "Welly",
tasks: [{
action: "Buy Flowers",
done: false
},
{
action: "Get Shoes",
done: false
},
{
action: "Collect Tickets",
done: true
},
{
action: "Call Joe",
done: false
}
]
};
},
computed: {
hidecompletedtask(){
return _.map(this.tasks,(val)=>{
return !val.done;
});
}
}
}
</script>
<style>
</style>
package.json
{
"name": "todo",
"version": "0.1.0",
"private": true,
"scripts": {
"serve": "vue-cli-service serve",
"build": "vue-cli-service build",
"lint": "vue-cli-service lint"
},
"dependencies": {
"bootstrap": "^4.4.1",
"core-js": "^3.4.4",
"jquery": "^3.4.1",
"lodash": "^4.17.15",
"popper.js": "^1.16.1",
"vue": "^2.6.10"
},
"devDependencies": {
"#vue/cli-plugin-babel": "^4.1.0",
"#vue/cli-plugin-eslint": "^4.1.0",
"#vue/cli-service": "^4.1.0",
"babel-eslint": "^10.0.3",
"eslint": "^5.16.0",
"eslint-plugin-vue": "^5.0.0",
"vue-template-compiler": "^2.6.10"
},
"eslintConfig": {
"root": true,
"env": {
"node": true
},
"extends": [
"plugin:vue/essential",
"eslint:recommended"
],
"rules": {},
"parserOptions": {
"parser": "babel-eslint"
}
},
"browserslist": [
"> 1%",
"last 2 versions"
]
}

Answer 1

You'll still need to access the prototype via the this context, like this._.map().
computed: {
hidecompletedtask() {
return this._.map(this.tasks, (val) => {
return !val.done;
});
}
}
Reference: Adding Instance Properties.
Alternatively, you could extend the global window object. Put the following line in your main.js (or some booting file).
window._ = require('lodash');
Somewhere else where you need the library:
computed: {
hidecompletedtask() {
// The underscore (_) character now refers to the `window._ object`
// so you can drop the `this`.
return _.map(this.tasks, (val) => {
return !val.done;
});
}
}

Answer 2

You can also use vue-lodash package -- Follow these steps:
npm install --save vue-lodash
in main.js -- import VueLodash from 'vue-lodash'
in main.js after import -- Vue.use(VueLodash)
Usage:
Vue._.random(20);
this._.random(20);
-------- OR ------------
In your main.js add this line of code:
window._ = require('lodash');
That way it will work without Vue or this:
Just do -- _.map()

Answer 3

You can import lodash in your main.js file by javascript window object like this:
window._ = require('lodash');
Then use it anywhere in your projet like this:
var original = [
{ label: 'private', value: 'private#johndoe.com' },
{ label: 'work', value: 'work#johndoe.com' }
];
var update = [
{ label: 'private', value: 'me#johndoe.com' },
{ label: 'school', value: 'schol#johndoe.com' }
];
var result = _.unionBy(update, original);
var sortedresult = _map(_.sortBy(result, 'label'));
console.log(sortedresult);
I just use lodash unionBy and sortBy method for example.