Trouble mapping array javascript

Question

So I'm trying to build a chart as a webcomponent and I'm having some trouble with mapping an array. The error says: this.values.map is not a function

Here is the code:

import {LitElement, html, css} from 'lit-element';


class ApexChart extends LitElement {

static get properties(){
    return{
        values: {Array},
        labels: {Array}
    };
}

constructor(){
    super();
    this.values = [];
    this.labels =[];
}

static get styles(){
    return css `

    `;
}

render(){
    return html`
         <p>${this.values.map(value => {value + 1})}</p>
    `;
}


}

customElements.define('apex-chart', ApexChart);

I'm passing the values from html

<apex-chart values="[1,2,3,4]" labels="['Hi', 'Hello', 'Oi', 'Hola']"></apex-chart>

I can't see what I'm doing wrong

Answer 1

You have two issues:

1) the properties type converter is not defined correctly. It should be:

static get properties(){
    return{
        values: { type: Array },
        labels: { type: Array }
    };
}

2) The map method isn't working correctly. Currently it returns undefined values because if you use {} you must use the return keyword.

> [0, 1].map(value => { value + 1 })
<- (2) [undefined, undefined]

Instead use:

render(){
    return html`
         <p>${this.values.map(value => value + 1)}</p>
    `;
}

Or:

render(){
    return html`
         <p>${this.values.map(value => { return value + 1; })}</p>
    `;
}