手写foreach
/**
* forEach(cb,thisArg)
* cb : (value: any, index: number, array: any[]) => void, thisArg?: any): void
* 接受第二个参数thisArg，只是定制forEach中this的指向, 并不影响传给回调函数中的三个参数
*/
Array.prototype._forEach = function (cb, thisArg) {
if (typeof cb !== 'function') {
throw 'the parameter cb must be a function'
}
if (!Array.isArray(this)) {
throw 'function _forEach must used by Array'
}
const arr = this
for (let index = 0; index < arr.length; index++) {
const v = arr[index];
cb.apply(thisArg, [v, index, arr])
}
}
Array(3).fill()._forEach(function (e) {
console.log(arguments,this);
})
