var deepCopy = function(src) {
    var ret = {}
    for (var k in src) {
        ret[k] = typeof src[k] ==='object' ? deepCopy(src[k]) : src[k]
    }
    return ret
}

This method has always been used for deep copy. Object.assgin can only deep copy the first layer. Deep copy is still a shallow copy. Just remember this

let obj3 = Object.assign({},obj1,{b:Object.assign({},obj1.b)});

let obj4 = JSON.parse(JSON.stringify(obj1));

Shallow copy: If the attribute element is a complex data type, the inner element copy reference;
slice, concat, jQury’s $.extend({},obj) are all shallow copies;
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