Introduction of JS Basics, annotations, variables, data types, and output syntax

Introduced:

Single, double line comments:

The output syntax of JS
Pop-up Window form alert ();

alert (123);

The effect is as follows:

The prompt () method is used to display a dialog box that prompts the user for input

Prompt (' Please enter name ');

The effect is as follows:

document.write () print in an HTML document

document.write (123);//Can be displayed directly in the document

The effect is as follows:

Console output: Console.log (); General as debug output statement

Console.log (123); Control Desk

The effect is as follows:

Variable:

Note the naming conventions:

JS inside: Letters, numbers, underscores, $ symbols, such as 4 components, the number can not be the beginning of the name of the content.
Hump method naming

Assignment value:

var i=0;
I=1;
alert (i);

The effect is as follows:

Data type:

Number

var I=1;
Alert (typeof (i));

The effect is as follows:

Character:

var i= "abc";
Alert (typeof (i));

The effect is as follows:

To determine the Boolean:

var i=true; False
Alert (typeof (i));

The effect is as follows:

No objects selected:

var i=0;
Alert (typeof (a));

The effect is as follows:

Array:

var obj=["AA", "BB", "CC"];
Alert (typeof (obj));

The effect is as follows:

Introduction to

JS basics, annotations, variables, data types, and output syntax