I am having a hard time understanding the following class declaration: it seems that element is default to undefined, but I have no idea why
(x, y) in the element = (x,y) => undefined necessary; is (x,y) a abbreviated way of specifying array elements inside element object?element(x, y) to access array elements inside element?class Matrix {
constructor(width, height, element = (x, y) => undefined) {
this.width = width;
this.height = height;
this.content = [];
for (let y = 0; y < height; y++) {
for (let x = 0; x < width; x++) {
this.content[y * width + x] = element(x, y);
}
}
}
let matrix = new Matrix(2, 2, (x, y) => `value ${x},${y}`);
The code is from Chapter 6 of Eloquent JS booke
element is being set to an arrow function expression that takes two arguments and returns undefined. This code would be equivalent:
constructor (width, height, element) {
if (!element) element = (x, y) => undefined
}
And these two are mostly equivalent with the scope caveat (this in the version with the function keyword refers to that function):
(x, y) => undefined
function (x, y) { return undefined }
Either way it's written, element is a function that, by default (if no third parameter is passed when instantiating an instance of that class), will take two parameters x and y and return undefined.
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