@extra-array/left-update/index.js

Gets values from the left.

'use strict';

/**
 * Gets zero-based index.
 * @param x an array
 * @param i index (-ve: from right) (0)
 */
function index(x, i = 0) {
    return i < 0 ? Math.max(x.length + i, 0) : Math.min(i, x.length);
}

/**
 * Gets index range of part of array.
 * @param x an array
 * @param i start index (-ve: from right) (0)
 * @param I end index (-ve: from right) (X)
 * @returns [start index, end index]
 */
function indexRange(x, i = 0, I = x.length) {
    i = index(x, i);
    I = Math.max(i, index(x, I));
    return [i, I];
}

/**
 * Counts the number of values.
 * @param x an array
 * @param i start index (-ve: from right) (0)
 * @param I end index (-ve: from right) (X)
 */
function size(x, i = 0, I = x.length) {
    var [i, I] = indexRange(x, i, I);
    return I - i;
}

/**
 * Gets a part of array.
 * @param x an array (updated)
 * @param i start index (0)
 * @param I end index (end)
 * @returns x
 */
function slice$(x, i = 0, I = x.length) {
    x.copyWithin(0, i, I);
    x.length = size(x, i, I);
    return x;
}

/**
 * Gets values from left.
 * @param x an array (updated)
 * @param n number of values (1)
 * @returns x
 */
function left$(x, n = 1) {
    return slice$(x, 0, n);
}

module.exports = left$;