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JavaScript code can be executed only through HTML/XHTML documents. There are two ways to do this.
1. Place the JavaScript code between the <script> labels in the <! DOCTYPE html PUBLIC "-// W3C // dtd xhtml 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<Html xmlns = "http://www.w3.org/1999/xhtml">
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = UTF-8"/>
<Title> untitled document </title>
<Script>
<! -- JavaScript Goes Here --> www.2cto.com
</Script>
</Head>
<Body>
</Body>
</Html>
2. Another better way is to save JavaScript code as an independent file with the extension. js. A typical practice is to place a <script> label in the <! DOCTYPE html PUBLIC "-// W3C // dtd xhtml 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<Html xmlns = "http://www.w3.org/1999/xhtml">
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = UTF-8"/>
<Title> untitled document </title>
<Script src = "file. js"> </script>
</Head>
<Body>
</Body>
</Html>
But the best practice is to put the <script> tag at the end of the HTML document, before the </body> tag:
<! DOCTYPE html PUBLIC "-// W3C // dtd xhtml 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<Html xmlns = "http://www.w3.org/1999/xhtml">
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = UTF-8"/>
<Title> untitled document </title>
</Head>
<Body>
<! -- Mark-up goes here -->
<Script src = "file. js"> </script>
</Body>
</Html>
Annotations in JavaScript
// Single line comment
<! -- Single line comment, no need to close
/*
Multi-line comment
*/
JavaScript is a weak type language. In other words, you do not need to specify the type of a variable. You can store variable values without worrying about its type.
Array initialization:
Var beatles = Array (4); limited length
Var beatles = Array ();
Beatles [0] = "John ";
Var beatles = Array ("A", "B", "C ");
Var beatles = ["A", 234, false];
Associated array: You can specify the subscript for each new element by filling in the array. A string can be used for the next mark.
Var lennon = Array ();
Lennon ["A"] = "John ";
Lennon-[ "B"] = 1209;
This method is not recommended.
Object:
Var lennon = Object ();
Lennon. name = "John ";
Lennon-year = "1940 ";
Var lennon = {name: "John", year: 1940 };
Naming: variables are separated by underscores (_), and functions use the hump naming method.
Comparison operators: = and! In JavaScript! = Is not strictly used. When you compare 3 = "3", the result is true. If you want to strictly compare them, you 'd better use = and! =
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