How to implement native map in js
JS native method map implementation, the code is as follows:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<meta name="author" content="杨欣">
<title>map</title>
</head>
<body>
<script>
Array.prototype.my_map = function (callback) {
if (!Array.isArray(this) || !this.length || typeof callback !== 'function') {
return []
} else {
let result = [];
for (let index = 0; index < this.length; index++) {
const element = this[index];
result.push(callback(element, index, this))
}
return result
}
}
let arr = [1, 2, 3, 4, 5]
let res = arr.my_map((ele, i) => {
return ele + 10
})
console.log(res)
</script>
</body>
</html>(Recommended tutorial: js tutorial)
Supplementary knowledge points :
We usually use the encapsulated map method. If we encapsulate a map ourselves, how should we implement it.
The basic principle remains unchanged. In fact, the core of traversing an array is the for loop. Therefore, a map method is encapsulated below.
The ideas are as follows:
1. Add a method to the prototype
2. Pass a function and this
3. The parameters passed by the call method are the same as those of the encapsulated map method.
Array.prototype.fakeMap = function(fn,context) {
let arr = this;
let temp = [];
for(let i=0;i<arr.length;i++){
let result = fn.call(context,arr[i],i,arr);
temp.push(result);
}
return temp;
}Recommended video tutorial: javascript video tutorial
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