Common Methods for parameter detection during function calling in Javascript

1. Method overload

JS does not directly support method overloading similar to C #, so it can only be solved in disguise.Code(Using the built-in attribute arguments)

 
VaR F1 = function (P1, P2, P3) {Switch (arguments. length) {Case 0: Alert ("F1 without Parameters") break; Case 1: Alert ("F1 with 1 parameter version:" + p1) break; Case 2: alert ("Two Parameter versions of F1:" + p1 + "," + p2) break; Case 3: Alert ("three parameter versions of F1: "+ p1 +", "+ p2 +", "+ P3) break; default: Alert (" more than three parameters cannot be called! "); Break;} F1 (); F1 (" 1 "); F1 (" A ", 100); F1 (" 1 "," 2 ", "3"); F1 ("1", "2", "3", "4 ")
 

2. Check the number of parameters

The JS engine does not forcibly check the number of parameters when calling the function, so it can only be processed by itself. Example code:

VaR fnmustoneparam = function (p) {// check whether there are any parameters passed in if (typeof P = "undefined") {alert ("fnmustoneparam must have parameters passed in, can be called (1 )! "); Return;} // You can also write it as if (arguments. Length = 0) {alert (" fnmustoneparam must have a parameter passed in before calling (2 )! "); Return;} // check the number of parameters if (arguments. length! = 0) {alert ("fnmustoneparam can be passed in only one parameter call! "); Return;} // to do...} // fnmustoneparam (1, 3, 4 );
 

3. Basic Parameter type detection
The JS engine does not detect the parameter type. If you want to limit the basic type of the parameter, you can use typeof to determine the basic type.

 
VaR fnstring = function (s) {If (arguments. length! = 1) {alert ("the number of parameters does not match! "); Return;} If (typeof s! = "String") {alert ("can only be a string type parameter! "); Return ;}// fnstring (123 );
 

4. Custom class parameter type detection
The method mentioned in Article 3rd can only detect the basic types of parameters. If a parameter of a custom class is used and the typeof operator number is used, only the object type detection result can be obtained, you can use the instanceof operator number to solve this problem.

 function person (name, age) {This. name = Name; this. age = age;} function fnperson (p) {If (arguments. length = 1 & P instanceof person) {// If (arguments. length = 1 & P. constructor = person) // You can also write alert ("fnperson called successfully, P. name = "+ P. name + ", p. age = "+ P. age);} else {alert ("You must input a person-type parameter before calling! ") ;}} Fnperson (" ASDF "); fnperson (new person ('yang Ta' under the bodhi tree, 30)