JS Basic Example

Creating variables

var Obj=value;

where obj is the variable name; The value means a number, an array, a function, etc.

Multi-variable calculation

var a1=200,b1= ' Hello ', c1=400;

var d1=c1-a1;//this is a simple calculation.

The main work of a variable is to save the right to the left of the equals sign

Console.log (obj); Enter the contents of obj, where obj means it may be an array, possibly a function.

Str.tostring () converted to string mode

typeof (obj): see what type of obj is

String (c): convert C to string

Number (x): limited to Pure digital turn

parseint (obj)/parsefloat (obj)

+ + before the first operation, to the new value

+ + in the After, first operation, to the old value

Short circuit Mode:obj&& (OBJ1)

Example

For example, whether the amount is greater than 500, more than 0.8

obj>=500&& (obj*=0.8)

Set default value: Value 1| | Value 2

Example

Console.log (reply| | ' Text ')

　　

Trinocular/Ternary

An expression? Action 1: Action 2

Example

A>1?consoel.log (a): 1

Strong ternary

An expression? Action 1: Expression? Action 2: Expression? Action 3: Default value;

Example

A>=2000> ' A ': a<7000? ' A+1 ': ' Hell ';

　　

Function Surface Questions

Function F1 () {1}

F1 ();

Function F1 () {2}

F1 ()

Note: If F1 () appears multiple times on the page, the previous function is overwritten

Result output 2,2

var f1= ';

F1 ();//error, because the variable name will never be a function

Declaring an advance issue

var n = 100;
function func () {
var n; Declaration in advance
Console.log (n);//?undefined
n = 99;
Console.log (n);//?99
}
Func ();
Console.log (n); ? 100

　　

Code: encodeURI (s); Decode: decodeURI (s)

Calculation or program

Eval (obj)

Switch (obj) {///Note: The expression in switch () brackets indicates that the = = = is all equal to the way

Case OBJ+1: statement body; break

Default

Statement body

}

var num = parseint (Prompt ("please button"));
Switch (num) {
Case 1:console.log ("in Query ...");
Case 2:
Case 3:console.log ("System maintenance:"); Break
Case 0:console.log ("Please Hang Up");
Default:console.log ("Invalid button");
}

Calculate the day ordinal of the current month

1: Write a function that determines if it is a leap year

function Getleapyear (y) {
if (y%4==0 && y%100!=0 | | (y%400==0)) {
return true;
}else{
return false;
}
}

2: Write a function for the current month

function GetDays (y,m,d) {

var x=getleapyear (y);

var s=x==true?29:28;

var days=0;

By comparing M with the past month, we conclude that the following

m>1&& (DAYS=DAYS+31);

m>1&& (Days=days+s);

... Written to around November

Days+=d;

Return days

}

Cycle examples

Sum

/1: Create variable save cumulative result sum 0
2: Create loop variable save start value I 2
3: Create loop Add judgment condition <= 100
4: Accumulate in the loop body

var sum=0;

for (Var i=1;i<=100;i++) {

Sum+=i

}sum

Ask 2+4+6+. Example of +100

for (Var i=2;i<=100;i+=2) {

The operation here is the same as the sum.

}

Compare size

function d (a,b,c) {

var max=a;

b>max&& (MAX=B);

c>max&& (MAX=C);

return Max;

}

Compare size in array

Function d (a) {

var max=a[0];

if (A[i]>max) {

Max=a[i]

}

　　

}

Determine if it is a letter, number, or other

if (a>= ' a ' && a<= ' z ') {}

if (a>=0&& a<=0) {}

else{}

Array comparison size

Arr.sort (function (b) {

Return A-B

})

Determine how many leap years between 2000 and 3000

1: The push () mode of the array

2: By creating a variable COUNRT

Then in judging leap year if under count++

Example

var count = 0;
for (Var i=2000;i<=3000;i++) {
if (i%4==0 && i%100!=0 | | (i%400==0)) {
count++;
}
}
Console.log (count);//243

When the number of statistics

var num = 0;//Save number
var CHS = 0;//Saves the number of letters 16:54----17:05
var cc = 0;
var other = 0;
for (Var i=0;i<str.length;i++) {
var c = Str.charat (i);
if (c >= ' 0 ' && C <= ' 9 ') {
num++;
}else if (c >= ' a ' && c <= ' z ') {
chs++;
}else if (c >= ' \u4e00 ' && c<= ' \u9fa5 ') {
cc++;
}else{
other++;
}
}
Console.log ("Number is the number is:" +num);
Console.log ("The number of letters is:" +chs);
Console.log ("The number of Chinese characters is:" +CC);
Console.log ("The other number is:" +other);

Prime

for (Var i=2;i<100;i++) {

for (Var j=2;j<i;j++) {

if (i%j==0) {

' Not prime number '

}

}

}

Mobile phone number Verification

/^ (+86|0086)? \s*1[3578]\d{9}$/

Mailbox

/^\[email protected]\w+\. [A-z0-9]+ (\.[ a-z]+)? $/

Str.replace (Regular or string, new value )

Str= ' 20160505 '

var d=/\d{4}\d{2}\d{2}/

Str.replace (d, ' $1$2$3 ');

JS Basic Example