Persistent data

} set(x, y, value) { this.content[y * this.width + x] = value;

The class stores its content in a single array of width × height elements. The elements are stored row by row, so, for example, the third element in the fifth row is (using zero-based indexing) stored at position 4 × width + 2.

The constructor function takes a width, a height, and an optional element function that will be used to fill in the initial values. There are get and set methods to retrieve and update elements in the matrix.

When looping over a matrix, you are usually interested in the position of the elements as well as the elements themselves, so we’ll have our iterator produce objects with x, y, and value properties.

class MatrixIterator { constructor(matrix) { this.x = 0; this.y = 0; this.matrix = matrix;

next() { if (this.y == this.matrix.height) return {done: true};

let value = {x: this.x, y: this.y, value: this.matrix.get(this.x, this.y)};

this.x++; if (this.x == this.matrix.width) { this.x = 0; this.y++;

} return {value, done: false};

The class tracks the progress of iterating over a matrix in its x and y properties. The next method starts by checking whether the bottom of the matrix has been reached. If it hasn’t, it first creates the object holding the current

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