Collapse of arrays

Trying to delete all the values in the ARR, the array collapsed during the loop;

1. One way to do this is to fall into a pit

var arr = ["a"."b"."c"."d"];
for(var i=0; i<arr.length; i++){ arr.splice(i,1);// Delete 1 element from I
}
 console.log(arr);// Is the result []? nonono.. His result is (2) [" B ", "D "]
// The array becomes ["b","c","d"] after the first element is deleted;
["b", "d"] ["b", "d"]
// I =2, but then the array is ["b", "d"], there is no 2 at all, the maximum is 1, so the loop stops.
(2) ["b", "d"];
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  1. How to solve array collapse? i–
var arr = ["a"."b"."c"."d"];
for(var i=0; i<arr.length; i++){ arr.splice(i,1);// Delete 1 element from II -;// The key is always to let I loop after entering for loop again with I =0 to start again
}
 console.log(arr);/ / perform []
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Deep copy

The first way

function copyObj(obj){  
var newObj = Array.isArray(obj)? [] : {};// create a new memory address
for(var key in obj){  // This loop can loop through both arrays and objects;
      if(typeof obj[key] === "object"){
          newObj[key] =  copyObj[key];
       }else{ newObj[key] = obj[key]; }}return newObj;
 }
        
var obj = {name:"Zhang".age:20};
var arr1 = copyObj(obj);  
console.log(arr1);// The object is passed in
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The performance of the second method is not as good as the first method above

Deep copy can be done with json.stringify and json.parse

1. Json.stringify converts an object to a JSON string

2. Json. parse converts JS strings into objects

3. But JSON: some attributes, such as undefined and function, will be ignored, and these elements will be discarded after copying, resulting in inaccuracy

var obj={
    name:"Zhang".age:20,}var res= JSON.stringify(obj);// Convert the obj object to a string
console.log(res);
var newObj=JSON.parse(res);// Convert the string to a new object
console.log(newObj);// It can be used for deep copy, which copies the same object as the original
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