JavaScript-programming skills-inert loading functions, javascript-programming skills

JavaScript-programming skills-inert loading functions, javascript-programming skills

Var testFunc = function () {if (typeof XMLHttpRequest! = 'Undefined') {testFunc = function () {alert ('1') ;}} else if (typeof ActiveXobject! = 'Undefined') {testFunc = function () {alert ('2') ;}} else {testFunc = function () {alert ('3 ');}}}

This function will execute judgment every time it is called. We hope this judgment can be executed only once in two ways.

The first method is to process the function when it is called. The Code is as follows:

Var testFunc = function () {if (typeof XMLHttpRequest! = 'Undefined') {testFunc = function () {alert ('1') ;}} else if (typeof ActiveXobject! = 'Undefined') {testFunc = function () {alert ('2') ;}} else {testFunc = function () {alert ('3 ');}}}

The second method is to process the function when it is loaded for the first time. The Code is as follows:

Var testFunc = (function () {if (typeof XMLHttpRequest! = 'Undefined') {return function () {alert ('1') ;}} else if (typeof ActiveXobject! = 'Undefined') {return function () {alert ('2') ;}} else {return function () {alert ('3 ');}}});

Both methods are supported.