JavaScript Pocket Reference

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JavaScript Pocket Reference

typeof

Return the type of the operand as a string. Evaluates to

“number”, “string”, “boolean”, “object”, “function”, or

“undefined”. Evaluates to “object” if the operand is

null.

instanceof

Evaluates to true if the object on the left was created

with the constructor function (such as

Date or RegExp)on

the right.

in

Evaluates to true if the object on the right has (or inher-

its) a property with the name on the left.

delete

Deletes an object property. Note that this is not the same

as simply setting the property to

null. Evaluates to false

if the property could not be deleted, or true otherwise.

void

Ignores the operand and evaluates to undefined.

Statements

A JavaScript program is a sequence of JavaScript statements.

Most JavaScript statements have the same syntax as the cor-

responding C, C++, and Java statements.

Expression statements

Every JavaScript expression can stand alone as a statement.

Assignments, method calls, increments, and decrements are

expression statements. For example:

s = "hello world";

x = Math.sqrt(4);

x++;

Compound statements

When a sequence of JavaScript statements is enclosed within

curly braces, it counts as a single compound statement. For

The JavaScript Language

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example, the body of a while loop consists of a single state-

ment. If you want the loop to ...