Common methods for parameter detection when calling javascript function_javascript skills

Copy code The code is as follows:

var f1 = function(p1,p2,p3){
switch(arguments.length){
case 0:
alert("no-parameter version of f1")
case 1:
alert("1 parameter version of f 1: " p1)
break;
case 2:
alert("2 parameter version of f1: " p1 ", " p2)
break;
case 3:
alert( "3-parameter version of f1: " p1 ", " p2 ", " p3)
     break;
    Default:
    alert("Calling with more than 3 parameters is not supported!");
                break; 2","3");
f1("1","2","3","4")


2. Parameter number detection
js engine is the same There is no forced check of the number of parameters when the function is called, so you can only handle it yourself. Sample code:

Copy code


Code As follows:

var fnMustOneParam = function(p){ //Check whether there are parameters passed in if (typeof p=="undefined"){ alert("fnMustOneParam must have parameters passed in before calling (1)!");

                                                                                                                                     ; {

      alert("fnMustOneParam must have parameters passed in before calling (2)!");
          return; !=0){
       alert("fnMustOneParam can only be called with one parameter!"); /fnMustOneParam(1,3,4);


3. Parameter basic type detection
The js engine will also not detect the type of parameters, if you want to make some restrictions on the basic types of parameters , you can use typeof to determine the basic type




Copy code


The code is as follows:


var fnString = function (s){
if (arguments.length!=1){
alert("Number of parameters does not match!");
return ;
}

if (typeof s != "string"){
       alert("Only string type parameters can be passed in!"); 🎜>

4. Parameter type detection of custom classes

The method mentioned in Article 3 can only detect the basic type of parameters. If it is a parameter of a custom class, if the typeof operator is used , only the type detection result of object can be obtained. In this case, the instanceof operator symbol can be used to solve the problem Copy code

The code is as follows: >

function Person(name,age){
this.name = name;
this.age = age;
}
function fnPerson(p){
if ( arguments.length=1 && p instanceof Person){
  alert("fnPerson was called successfully, p.name=" p.name ",p.age=" p.age);
  }
 else{
Alert ("You must pass in a parameter of a Person type to call!"); Yang Guo',30))