4. forEach()
Function:
forEach(callback, thisArg)Usage:
arr.forEach((ele, index, arr)=>{...}, this)Description: callback function will execute on every element. But not for uninitialized elements for sparse arrays.
Polyfill: forEach
//function returns undefined
Function.prototype.customForEach = function (callback) {
//this should point to array
if(Array.isArray(this)) {
for (let i = 0; i < this.length; i++) {
//check if each element exists
if(typeof this[i] !== 'undefined') {
//callback will take element, index and array as parameters
callback(this[i], i, this);
}
}
}
};
5. Keys()
Function:
keys(obj)Usage:
Obj.keys(anyobj)Description: returns array iterator
Polyfill:Keys
//function returns Array Iterator
Array.prototype.customKeys = function () {
let keys = [];
for (let i = 0; i < this.length; i++) {
keys.push(i);
}
// A generator function which returns a generator object( basically follows iterator protocol)
// Why we use here? because the keys return array iterator
// A yield will pause and resume the function (Basically will return the keys one by one until done becomes true)
function* iterator() {
yield* keys;
}
return iterator();
};
6. Values()
Function:
values(obj)Usage:
Obj.values(anyobj)Description: returns array iterator
Polyfill:Values
//function returns Array Iterator
Array.prototype.customValues = function () {
let values = [];
for (let i = 0; i < this.length; i++) {
values.push(this[i]);
}
// A generator function which returns a generator object( basically follows iterator protocol)
// Why we use here? because the values return array iterator
// A yield will pause and resume the function (Basically will return the values one by one until done becomes true)
function* iterator() {
yield* values;
}
return iterator();
};
7. Entries()
Function:
entries(obj)Usage:
Obj.entries(anyobj)Description: returns array iterator
Polyfill:Entries
//function returns Array Iterator
Array.prototype.customEntries = function () {
let entries = [];
for (let i = 0; i < this.length; i++) {
entries.push(i, this[i]);
}
// A generator function which returns a generator object( basically follows iterator protocol)
// Why we use here? because the entries return array iterator
// A yield will pause and resume the function (Basically will return the entries one by one until done becomes true)
function* iterator() {
yield* entries;
}
return iterator();
};
Stay Tuned for Part 3 Keep Learning!