The existence of functions and parameter issues in JavaScript's jQuery library_jquery

jQuery function parameter passing

Using external variables in jQuery’s function:

//如何取得i的变量
for(i=0;i<3;i++) {
 $.get("/test.html", function(data){
  alert(i)
 });
}


//使用闭包：
for(i=0;i<3;i++) {
 (function(index){
  $.get("/test.html", function(data){
  alert(index)
  });
 })(i)
}

JavaScript and jQuery detect whether a function exists

The method to detect whether a function exists in JavaScript is:

if(typeof $form.validate == 'function') {
 console.log('该 function 存在');
} else {
 console.log('该 function 不存在');
}

For example: Need to detect whether an MD5 method exists:

if(typeof window.md5 == 'function') {
 // 如果纯在该方法，才去调用
 md5(286);
}

To detect whether a jQuery method exists, you can use the following method:

if( jQuery.isFunction(jQuery.fn.rtFunction) ) {
 // 如果该方法存在，才去调用
 jQuery(document).rtFunction();
}