Javascipt Basic Content--details to be noted

Last Update:2017-01-19 Source: Internet

Author: User

Tags logical operators

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javascipt-Basic ---details need to be noted:

1, special values : NaN, Infinity, isNaN (), Isfinite ()

NaN:

Copy Code code as follows:

var a=parseint (' A123 ');
Window.alert (a); Output Nan

Infinity:

Copy Code code as follows:

Window.alert (6/0);//Output Infinity infinity (best not to write)

isNaN (): Judge whether the number, not the number returns TRUE, the number returns false

Copy Code code as follows:

var a= "DD";
Window.alert (isNaN (a)); Returns True

Isfinite (): Used to determine whether infinity. Returns False if number is NaN (not a number), or is a positive or negative infinity.

Copy Code code as follows:

Window.alert (Isfinite (6/1)); Returns True
Window.alert (Isfinite (6/0)); return False

2. Logical operators:

In a logical operation, 0, "", false, null, undefined, and nan all represent false

(or | | ) | | Returns the first value that is not false (the object is also available), or the last value (if all false)

This knowledge point is used a lot in the JavaScript framework.

Copy Code code as follows:

var a=true;
var B=false;
var C=b | | A

Window.alert (c); Output true

Copy Code code as follows:

var a=2;
var b=0
var c= a | | b

Window.alert (c); Returns the first value, Output 2

Copy Code code as follows:

var A=false;
var b= "";
var c = 0;
var d =new Object (); Object

var Aa=a | | B | | C | | D; A,b,c is all false this returns D
Window.alert (AA); Return D (Object)

4. Multi-branch Switch

Copy Code code as follows:

var flag=1;

Switch (flag) {

Default
Window.alert ("nothing");

Case ' a ':
Window.alert ("a");

Case ' B ':
Window.alert ("B"); No break statement, no match succeeded, at which time the result is output

}

Copy Code code as follows:

var flag=1;

Switch (flag) {

Default
Window.alert ("nothing");

Case ' a ':
Window.alert ("a");

Case 1:
Window.alert ("B"); No break statement when the match succeeds then the break statement is not found at this time output b

}

5. Function call

Func.js

Copy Code code as follows:

Function ABC (val) {

Window.alert ("ABC ()" +val);
}

Functions that have return values
function test (num1,num2) {

var res=0;
Res =num1+num2;

return res;
}

Functions that do not return a value
function Noval (num1,num2) {

var res=0;
res=num1+num2;
}

Function call:

Copy Code code as follows:

Function Call 2---variable = functions name; Call when called: variable (actual argument)
var test1=abc; At this point the variable is equivalent to a function reference (pointer)
Window.alert (ABC); Output ABC the entire function code, you can understand
Test1 (500);

If the called function has a return value, it can be returned directly in the program without a return value but you received it, which is returned to undefined
Calling functions that have return values
var res=test (20,40);
Window.alert (RES);

Call function with no return value
Window.alert ("Call function with no return value");
var res=noval (1,1);
The output undefined at this time
Window.alert (RES);

</script>
<body></body>

JS supports functions with variable number of parameters

Copy Code code as follows:

Function call-Recursive

/* Function ABC (num) {

if (num>3) {

ABC (--NUM);
}
Document.writeln (num);
}

Call function
ABC (5); Output 3 3 4
*/

JS supports functions with variable number of parameters

Function abc () {
JS provides a arguments that can be accessed so the values passed in
Window.alert (arguments.length); Incoming number of
Iterate through the arguments passed in
for (Var i=0;i<arguments.length;i++) {

Window.alert (Arguments[i]);
}
}

Call
Window.alert ("ABC (12,13,\" hello\ ", 56)");
ABC (12,13, "Hello", 56)

Window.alert ("ABC (5)");
ABC (5);

Window.alert ("ABC ()");
ABC ();
</script>
<body></body>

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