JavaScript study notes (7) Introduction to js functions_basic knowledge

1. The internal attribute arguments
arguments of the function is used to save the parameters of the function. arguments.callee points to the function owning the arguments object

Copy code The code is as follows:

//Factorial
function factorial(num) {
if (num return 1;
} else {
return num*arguments.callee(num-1); //Replace
} with agreements.callee
}

var trueFactory = factorial;
factorial = function {
return 0;
}
alert(trueFactorial(5)); //20
alert(factorial(5)); //0

2. Function attributes and method
length attribute, indicating the number of function parameters

3. apply() and call() methods
apply() and call() methods are used to pass parameters or expand functions Scope

Copy code The code is as follows:

//Pass parameters
function sum( num1,num2) {
return num1 num2;
}
function callSum(num1,num2) {
return sum.call(this,num1,num2); //The first parameter this, List all parameters later
}
alert(callSum(10,10)); //20

function calSum1(num1,num2) {
return sum.apply(this,arguments) ; //The first parameter this, the second parameter arguments
}
function calSum2(num1,num2) {
return sum.apply(this,[num1,num2]); //First parameter this, the second parameter is the parameter array
}
alert(callSum1(10,10)); //20
alert(callSum2(10,10)); //20

Copy code The code is as follows:

//Change function scope
window.color = "red";
var o = { color:"blue"};
function sayColor() {
alert(this.color);
}
sayColor() ; //red
sayColor.call(this); //red
sayColor.call(window); //red
sayColor.call(o); //blue