1. What are closures?

A closure is a function that accesses a variable in another function and is called a closure. function a(propName){ return function(){ return propName}}

2. What causes closures?

Closures are related to scope chains. Code will form a scope chain when executed. Function A has closure B, and the closure B’s scope chain will hold variables referenced by function A. The scope of a closure includes the scope of the closure itself, the scope of external functions, and the scope of the global environment

3. Closure disadvantages

Closure disadvantage 1: Referencing variables can hog memory and affect program quality. Closure disadvantage 2: The object variable referenced by the closure is the last value of that variable, so the variable is not necessarily in its current state.

function createFunctions() {

var result = new Array(a);for (var i = 0; i < 10; i++) {

result[i] = function () {

return i;

};

}

return result;

}

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They both refer to the same variable I, so they both return 10

4. Closures and this

This is usually the execution environment of a function, and in closures this is usually the global environment.

var name = "The Window";

var object = { name: "My Object".getNameFunc: function () {

return function () { return this.name; }; }}; alert(object.getNameFunc()());//"The Window"
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Reason: Each function can only access its own this and arguments, and this in a closure cannot be searched for in an external function.