I am trying to implement my version of forEach to make sure I understand it correctly, however, since the callback provided to forEach can accept 1, 2 or 3 arguments I need to figure out a way to check the number of arguments.
For example, here's what I currently have:
Array.prototype.myForEach = (callback) => {
//console.log(callback.arguments.length, "arguments supplied to callback") This doesn't work.
//Check the number of arguments provided to the callback
if(typeof callback === 'function') {
for(var i = 0; i < this.length; i ) {
//If single argument then callback(this[i]) should be invoked.
callback(this[i], i, this)
}
}
else throw new Error("Callback for myForEach is not a function")
}
What I aim to achieve is:
arr.myForEach((a, b) => {} //a should refer to element, b to the index, c to the array
CodePudding user response：
While you can check the number of arguments provided by checking the .length property of the function:
Array.prototype.myForEach = (callback) => {
console.log(callback.length);
};
[].myForEach((arg1, arg2) => {});
[].myForEach((arg1) => {});It's not needed here - there's no problem with passing all arguments regardless of the callback uses them or not (and if the callback accepts more than 3 arguments, for some odd reason, they'll be undefined inside the callback, just like with forEach).
Array.prototype.myForEach = function(callback) {
if (typeof callback !== 'function') {
throw new Error("Callback for myForEach is not a function")
}
for(var i = 0; i < this.length; i ) {
callback(this[i], i, this);
}
};
['a', 'b'].myForEach((item, i, arr) => {
console.log(item);
console.log(i);
console.log(arr);
});CodePudding user response：
The number of arguments passed will be reflected by the callback.length
Array.prototype.myForEach = (callback) => {
console.log(callback.length);
}
const arr = [1,1];
arr.myForEach((arg1, arg2, arg3) => {}); //3
arr.myForEach((arg1, arg2, arg3, arg4) => {}); //4
arr.myForEach((arg1, arg2, arg3, arg4, arg5) => {}); //5