Java Script What is a closure?

Suppose you now have a function f (x) = a + X

This function is not complete, such as f (1) = a + 1

You have one question: How much is a?

There are two ways to answer this question

The first is called "Dynamic Scope", and the value of a is determined by the value of a in the context of a function call , such as

A = 1;
V=f (1); here V is 2

The problem with dynamic scopes is that each time a function invokes the same parameter, it may not return the same value, and the return value depends on some value of the context

The second type is the lexical scope, and the value of a depends on the value in the context of the function definition .

G (a) = lambda (x) a + x;
f = g (2)

Here the function g returns a function like the above function f, where A is 2, then executes

A = 1;
V=f (1); here V is 3

Because F wants to "remember" the value of a when it is defined by itself is 2, so when implemented

f (x) = a + x and a = 2 are packaged in a block, called "closures", meaning that it is completely independent, relying only on invocation-time parameter evaluation, no longer dependent on the context of the call

Baozii
Links: https://www.zhihu.com/question/21865351/answer/20823147
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Java Script What is a closure?