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Define several types of functions in JavaScript: 1, use the function keyword to define the function through a declaration or expression, the syntax is "function functionName (parameters) {executed code}"; 2, use the function constructor Function () to construct the function.

The operating environment of this tutorial: windows10 system, javascript1.8.5 version, Dell G3 computer.

What are several types of functions defined by javascript

JavaScript uses the keyword function to define functions.

A function can be defined by a declaration or an expression.

Function declaration

In the previous tutorial, you learned about the syntax of function declarations:

Function functionName (parameters) {Code executed}

The function will not be executed immediately after it is declared, but will be called when we need it.

Function constructor

The function constructor is used to create a function object, and virtually every function in JavaScript is a function object.

The syntax of the function constructor:

New Function ([arg1 [, arg2 [,... argN]],] functionBody)

Arg1, arg2,... ArgN is used as the variable name of the normal parameter name of the function, which must be a string that conforms to the JavaScript variable identification specification to represent a single variable or a comma-separated string that represents multiple variables, such as "x", "theValue", and or "aline b".

FunctionBody contains a string of JavaScript statements defined by the function.

Description

1. A function object is created when the function constructor is parsed into a function. But this is less efficient than using function declarations, function expressions, and so on, because these functions are parsed directly by code.

two。 The string parameters passed to the function constructor are treated as the variable parameter names of the function generated by the function constructor, in the order in which they appear as the parameters of the generated function.

3. Calling the function constructor in the form of a function (which doesn't work or modified with the new keyword) has the same effect.

Examples

/ / Example can be run directly in your JavaScript console// Create a function that takes two arguments and returns the sum of those argumentsvar adder = new Function ('await,' baked, 'return a + b'); / / Call the functionadder (2,6); / / > 8

Parameters an and b are normal parameter names that can be used inside the function body.

The generated function is:

Function (aformab) {undefined return aforb;}

A way to parse json: var json = (new Function ("return" + str)) ()

The principle is the same

The generated function is:

Function toJson (str) {undefined return str;} var str= "{'aqiaqizhuo 1"; toJson (str)

That is, function () {return {'axiaqizhuo 1jinghuanghuanghuanghuanghuanghuanghuanghuanfangbang (abc'}}).

The difference between function constructors and function declarations:

Functions created with function constructors do not create closures in context, they are always created in global scope, and when executing the created function, they can only use their own local or global variables, unlike eval.

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