Here is a quick reference to many of the basic handles and definitions for the JavaScript language.
| Comparision and conditional operators | |||
| Name | Operator | Description | |
| Equal | == | Returns true if the operands are equal | |
| Strict equal | === | Returns true if the operands are equal and of the same type | |
| Not equal | != | Returns true if the operands are not equal | |
| Strict not equal | !== | Returns true if the operands are not equal or not of the same type | |
| Greater than | > | Returns true if the left operand is greater than the right operand | |
| Les than | < | Returns true if the left operand is less than the right operand | |
| Greater than or equal | >= | Returns true if the left operand is greater than or qual to the right operand | |
| Less than or equal | <= | Returns true if the left operand is less than tor euqal to the right operand | |
| Assignment Operators | |||
| Assignment | = | Assigns the value of the right operand to the left operand | |
| Compound addition assignment | += | Combines the value of the right operand with the value of the left operand or adds the value of the right operand to the value of the left operand and assigns the new value to the left operand | |
| Compound subtraction assignment | -= | Subtracts the value of the right operand from the value of the left operand and assigns the new value to the left operand | |
| Compound multiplication assignment | *= | Multiplies the value of the right operand by the value of the left operand and assigns the new value to the left operand | |
| Compound division assignment | /= | Divides the value of the left operand by the value of the right operand and assigns the new value to the left operand | |
| Compound modulus assignment | %= | Divides the value of the left operand by the value of the right operand and assigns the remainder (the modulus) to the left operand | |
| Data Types | ||
| Number | Positive or negative numbers with or without decimal places, or number written using exponential notation | |
| Boolean | A logical value of true or false | |
| String | Text such as "Hello World" | |
| Undefined | A variable that has never had a value assigned to it, has not been declared, or does not exist | |
| Null | An empty value | |
| Building Expressions | ||||
| Operator type | Operators | Description | ||
| Arithmetic | addition(+), subtraction(-), multiplication(*), division(/), modulus(%), increment(++), decrement(--), negation(-) | Used for performing mathematical calculations | ||
| Assignment | assignment (=), compound addition assignment (+=), compound subtraction assignment (-=), compound multiplication assignment (*=), compound division assignment (/=), compound modulus assignment (%=) | Assigns values to variables | ||
| Comparison | equal (==), strict equal (===), not equal (!=), strict not equal (!==), greater than (>), less than (<), greater than or equal to (>=), less than or equal to (<=) | Compares orperands and returns a Boolean value | ||
| Logical | and (&&), or (||), not (!) | Used for performing Boolean operations on Boolean operands | ||
| String | concatenation operator (+), compound assignment operator (+=) | Performs operation on astrings | ||
| Special | property access (.), array index ([]), function call (()), comma (,), conditional expression (?:), delete (delete), property exists (in), object type (instancedof), new object (new), data type (typeof), void (void) | Used for various purposes and do not fit within other operator categories | ||
| Arithmetic Binary Operators | |||
| Addition | + | Adds two operands | |
| Subtraction | - | Subtracts one operand from another operand | |
| Multiplication | * | Multiplies one operand by another operand | |
| Division | / | Divides one operand by another operand | |
| Modulus | % | Divides one operand by another operand and returns the remainder | |
| Arithmetic Unary Operators | |||
| Increment | ++ | Increases an operand by a value of one | |
| Decrement | -- | Decreases an operand by a value of one | |
| Negation | - | Returns the oposite value (negative or opsitive) of an operand | |
| Assignment Operators | |||
| Assignment | = | Assigns the value of the right operand to the left operand | |
| Compound addition assignment | += | Combines the value of the right operand with the value of the left operand or adds the value of the right operand to the value of the left operand and assigns the new value to the left operand | |
| Compound subtraction assignment | -= | Subtracts the value of the right operand from the value of the left operand and assigns the new value to the left operand | |
| Compound multiplication assignment | *= | Multiplies the value of the right operand by the value of the left operand and assigns the new value to the left operand | |
| Compound division assignment | /= | Divides the value of the left operand by the value of the right operand and assigns the new value to the left operand | |
| Compound modulus assignment | %= | Divides the value of the left operand by the value of the right operand and assigns the remainder (the modulus) to the left operand | |
| Comparision and conditional operators | |||
| Name | Operator | Description | |
| Equal | == | Returns true if the operands are equal | |
| Strict equal | === | Returns true if the operands are equal and of the same type | |
| Not equal | != | Returns true if the operands are not equal | |
| Strict not equal | !== | Returns true if the operands are not equal or not of the same type | |
| Greater than | > | Returns true if the left operand is greater than the right operand | |
| Les than | < | Returns true if the left operand is less than the right operand | |
| Greater than or equal | >= | Returns true if the left operand is greater than or qual to the right operand | |
| Less than or equal | <= | Returns true if the left operand is less than tor euqal to the right operand | |
| Logical Operators | |||
| Name | Operator | Description | |
| And | && | Returns true if both the left operand and right operand return a vlue of true; otherwise, it returns a value of false | |
| Or | || | Returns true if either the left operand or right opernad returns a value of true; if neither operand returns a value of true, then the expression containing the or || operator returns a value of false | |
| Not | ! | Returns true if an expression is false and returns false if an expression is true | |
| Escape sequence | |||
| Escape sequence | Character | ||
| \\ | Backslash | ||
| \b | Backspace | ||
| \r | Carriage return | ||
| \" | Double quotation mark | ||
| \f | Form feed | ||
| \t | Horizontal tab | ||
| \n | New line | ||
| \o | Null character | ||
| \' | Single quotation mark | ||
| \v | Vertical tab | ||
| \XXX | Latin-1 character specified by the XX characters, which represent two hexadecimal digits | ||
| \XXXXX | Unicode character specified by the XXXX characters, which represent four dexadecimal digits | ||
| Special Operators | |||
| Name | Operator | Description | |
| Property access | . | Appends an object, method, or property to another object | |
| Array index | [] | Accesses an element of an array | |
| Function call | () | Calls up functions or changes the order in which individual operations in an expression are evaluated | |
| Comma | , | Allows you to include multiple expressions in the same statement | |
| Conditional expression | ?: | Executes one of two expressions based on the results of a conditional expression | |
| Delete | delete | Deletes array elements, variables created without the var keyword, and properties of custom objects | |
| Property exists | in | Returns a value of true if a specified property is contained within an object | |
| Object type | instanceof | Returns true if an object is of a specified object type | |
| New object | new | Creates a new instance of a user-defined object type or a predefined JavaScript object type | |
| Data type | typeof | Determines the data type of a variable | |
| Void | void | Evaluates an expressions without returning a result | |
| Values returned by typeof operator | ||
| Return value | Returned for | |
| Number | Integers and floating-point numbers | |
| String | Text strings | |
| Boolean | True or false | |
| Object | Objects, arrays, and null variables | |
| Function | Functions | |
| Undefined | Undefined variables | |
| Understanding Operator Precedence | |||
| Operators | Description | Associativity | |
| . | Objects-highest precedence | Left to right | |
| [] | Array elements-highest precedence | Left to right | |
| () | Functions/evaluation-highest precedence | Left to right | |
| * / % | Multiplication/Division/Modulus | Left to right | |
| + - | Addition/subtraction/concatenation | Left to right | |
| < <= > >= | Comparison | Left to right | |
| instanceof | Object type | Left to right | |
| instanceof | Object property | Left to right | |
| == != === !== | Equality | Left to right | |
| && | Logical and | Left to right | |
| || | Logical or | Left to right | |
| , | Comma-lowest precedence | Left to right | |
| new | New object-highest precedence | Right to left | |
| ! | Not | Right to left | |
| - | Unary negation | Right to left | |
| ++ | Increment | Right to left | |
| -- | Decrement | Right to left | |
| typeof | Data type | Right to left | |
| void | void | Right to left | |
| delete | Delete object | Right to left | |
| ?: | Conditional | Right to left | |
| = += -= *= /= %= | Compound assignment | Right to left | |