Detailed analysis of JavaScript function definitions and javascript function definitions

Detailed analysis of JavaScript function definitions and javascript function definitions

Function

Key points:

A). functions are first-class citizens (importance) in javascript)
B). A function is an object.
C). The function defines an independent variable scope.

Definition Method

A) Name function:

Unless defined in another function, the name function is global.

// Global name function add (x, y) {return x + y;} console.info (add (100,200); // 300

B) Anonymous functions:

An anonymous function is usually assigned to a variable and called through the variable.

    var func = function (x, y) {      return x + y;    }    console.info(func(5, 2)); //7

Anonymous functions are applicable to the following "anonymous functions executed immediately:

Console.info (function (x, y) {return x + y;} (100,200) // call now );

C) The definition method affects the code execution result.

The name function can be used before being defined.

    console.info(sum(10, 10));    function sum(num1, num2) {      return num1 + num2;    }

The anonymous function must be defined before use.

    //console.info(sumFunc(10, 10));  //Uncaught TypeError: Property 'sumFunc' of object [object Object] is not a function     var sumFunc = function (num1, num2) {      return num1 + num2;    };    console.info(sumFunc(10, 10));

Function return value:

Return Value is generated using return. If no return is returned, the function returns undefined.

Function func () {} console.info (func (); // undefined function func2 () {return; // NULL return statement} console.info (func2 (); // undefined

The pitfalls hidden in return:

 var func = function (x, y) {   var sum = x + y;   return {     value : sum   } }

There is no problem with this writing: the Object {value: 10} returned by calling func (5, 5}

However:

  var func = function (x, y) {    var sum = x + y;    return    {      value: sum    };  }  console.info(func(5,5)); //undefined

If return is followed by a carriage return,
Call func (5, 5) to display undefined
The editor adds a semicolon after return. However, in this case, there is no use.

Functions are objects:

Function add (x, y) {return x + y;} console.info (add (100,200); // 300 var other = add; // other and add reference the same function object console.info (other (300,400); // 700 console.info (typeof other); // function console.info (add = other ); // true

Nested defined functions:

Within a function, you can define another function.

  function outerFunc(a, b) {    function innerFunc(x) {      return x * x;    }    return Math.sqrt(innerFunc(a) + innerFunc(b));  }  console.info(outerFunc(3, 4)); //5

Access external variables:

Internal functions can access external variables and parameters.

 var globalStr = 'globalStr'; function outerFunc2(argu) {   var localVar = 100;   function innerFunc2() {     localVar++;     console.info(argu + ":" + localVar + ":" + globalStr);   }   innerFunc2(); //hello:101:globalStr } outerFunc2("hello");

Function of the returned function:

Because the function is an object, it can be used as the return value.

  function outerFunc(x) {    var y = 100;    return function innerFunc() {      console.info(x + y);    }  }  outerFunc(10)(); //110

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