問(wèn)題描述

之前一直認(rèn)為代碼中使用==會(huì)讓使用或閱讀代碼者考慮隱式轉(zhuǎn)換，增加使用負(fù)擔(dān)（基本沒(méi)有好處？），那么lodash的slice方法是出于什么考慮使用==的呢？下面是源碼

/** * Creates a slice of `array` from `start` up to, but not including, `end`. * * **Note:** This method is used instead of * [`Array#slice`](https://mdn.io/Array/slice) to ensure dense arrays are * returned. * * @since 3.0.0 * @category Array * @param {Array} array The array to slice. * @param {number} [start=0] The start position. * @param {number} [end=array.length] The end position. * @returns {Array} Returns the slice of `array`. */function slice(array, start, end) { let length = array == null ? 0 : array.length if (!length) { return [] } start = start == null ? 0 : start end = end === undefined ? length : end if (start < 0) { start = -start > length ? 0 : (length + start) } end = end > length ? length : end if (end < 0) { end += length } length = start > end ? 0 : ((end - start) >>> 0) start >>>= 0 let index = -1 const result = new Array(length) while (++index < length) { result[index] = array[index + start] } return result}export default slice

問(wèn)題解答

foo == null 是 == 運(yùn)算符比較特殊的一種用法，實(shí)際上等價(jià)于 foo === null || foo === undefined，可以算是一種簡(jiǎn)寫(xiě)形式，這是由 == 運(yùn)算符的運(yùn)算規(guī)則決定的：