Deep copy

1. The JSON conversion:

var targetObj = JSON.parse(JSON.stringify(copyObj))
let arr4 = JSON.parse(JSON.stringify(arr))
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Disadvantages:

1. If an object has a function in it, the function cannot be copied
2. Unable to copy properties and methods on the copyObj object prototype chain
3. When the data level is very deep, stack overflow occurs

2. Ordinary recursive functions:

function deepCopy( source ) {
if(! isObject(source))return source; // Return if it is not an object
    let target = Array.isArray( source ) ? [] : {} // Array compatibility
    for ( let k in source ) {
    	if (source.hasOwnProperty(k)) {// Copy only the properties of the object itself
    		if ( typeof source[ k ] === 'object' ) {
            	target[ k ] = deepCopy( source[ k ] )
        	} else {
            	target[ k ] = source[ k ]
        	}
    	}
    }
    return target	
}

function isObject(obj) {
    return typeof obj === 'object'&& obj ! = =null
}
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Disadvantages:

1. Unable to hold a reference
2. When the data level is very deep, stack overflow occurs

3. Anti-stack overflow function:

function cloneLoop(x) {
    const root = {};
    / / stack
    const loopList = [
        {
            parent: root,
            key: undefined.data: x,
        }
    ];
    while(loopList.length) {
        // Depth first
        const node = loopList.pop();
        const parent = node.parent;
        const key = node.key;
        const data = node.data;

        // Initialize the assignment target. If key is undefined, copy it to the parent element, otherwise copy it to the child element
        let res = parent;
        if (typeofkey ! = ='undefined') {
            res = parent[key] = {};
        }
        for(let k in data) {
            if (data.hasOwnProperty(k)) {
                if (typeof data[k] === 'object') {
                    // Next loop
                    loopList.push({
                        parent: res,
                        key: k,
                        data: data[k],
                    });
                } else{ res[k] = data[k]; }}}}return root;
}
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