扩展原生Number

今天看你不知道的js 第三章有个比较有意思的方法，特记录一下。

if (!Number.prototype[Symbol.iterator]) {
	Object.defineProperty(
		Number.prototype,
		Symbol.iterator,
		{
			writable: true,
			configurable: true,
			enumerable: false,
			value: function iterator(){
				var i, inc, done = false, top = +this;

				// iterate positively or negatively?
				inc = 1 * (top < 0 ? -1 : 1);

				return {
					// make the iterator itself an iterable!
					[Symbol.iterator](){ return this; },

					next() {
						if (!done) {
							// initial iteration always 0
							if (i == null) {
								i = 0;
							}
							// iterating positively
							else if (top >= 0) {
								i = Math.min(top,i + inc);
							}
							// iterating negatively
							else {
								i = Math.max(top,i + inc);
							}

							// done after this iteration?
							if (i == top) done = true;

							return { value: i, done: false };
						}
						else {
							return { done: true };
						}
					}
				};
			}
		}
	);
}

用法

for (var i of 3) {
	console.log( i );
}
// 0 1 2 3

[...-3];				// [0,-1,-2,-3]