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Assignment Operators

• =. 
• The rest are "short hand" for x = x operator y.
  • +=.
  • -=.
  • *=.
  • /= .
  • %= .
  • <<= .
  • >>= .
  • >>>= .
  • &= .
  • ^= .
  • |= .

Arithmetic Operators

• +. Addition.
• -. Subtraction.
• *. Multiplication.
• /. Division.
• %. Modulus: return integer remainder. EG: 13 % 5 returns 3.
• ++. Unary increment operator. Can be used before the operand to return the new result, or after the operand to return the old result.
• --. Unary decrement operator. Can be used before or after the operand.
• -. Unary operator. Changes sign of operand.

Bitwise Operators

These convert operand(s) to 32 bits and then perform work on them. In the examples provided, the binary is shown instead of the decimal, for the sake of visual clarity.

• &. Bitwise AND, returns 1s for bit positions where both operands are 1, eg 10 & 12 yields 8, since 1010 and 1100 yields 1000.
• |. Bitwise OR, returns 1s for bit positions where either operand is 1. EG: 10 | 12 yields 14, since 1010 and 1100 yields 1110.
• ^. Bitwise XOR, returns 1s for bit positions where either operand is 1 but not both. EG: 10 ^ 12 yields 6, since 1010 and 1100 yields 0110.
• ~. Bitwise NOT, inverts the operand, eg. ~10 yields 5, since 1010 yields 0101.
• <<. Shift binary a to the left b places and pad the right side with b 0s. EG: 9 << 2 yields 36 since 1001 becomes 100100.
• >>. Shift binary a to the right b places and discard the b rightmost digits. EG: 9 >> 2 yields 2 because 1001 becomes 10.
• >>>. Shift binary a to the right b places and discard the b rightmost digits then pad the left with 0s. EG: 9 >> 2 yields 2 because 1001 becomes 10. For non-negative numbers, >> and >>> yield the same results.

Logical Operators

These are typically used with Boolean operands to return Boolean values but after JS 1.1, these operators can also be used to return one of the operands. This "fancy" feature makes the order of operands relevant!

• &&. And, returns a if a is false, other wise returns b. EGs:
  • true && false yields false .
  • false && "dog" yields false .
  • "dog" && false yields false .
  • "cat" && "dog" yields "dog" !
• ||. Or, returns a if a is true, other wise returns b. EGs:
  • true || false yields true .
  • false || "dog" yields dog .
  • "dog" && false yields "dog" .
  • "cat" || "dog" yields "cat" !
• !. Not, inverts the operand. EG: !true yields false.

Comparison Operators

NaN is not equal to anything, including NaN. Null and Undefined are equal.

• ==. Equal. True if operand values are equal. A data type conversion is performed if needed. EG: 5=="5" returns true. Objects must have same address space. EG: a1=new a; a2=new a; thus a1==a2 returns false.
• !=. Not equal.
• ===. Strict equal. True if operand values and data types are equal. EG: 5==="5" returns false. Objects must have same address space. EG: a1=new a; a2=new a; thus a1===a2 returns false.
• !==. Strict not equal.
• >.
• <.
• >=.
• <=.

String Operators

• +. Note that the plus sign is used as both an arithmetic and a string operator. EGs:

  8 + 8        // 16
  "8" + 8      // "88"
  8 + "8"      // "88"
  "8" + "8"    // "88"
  8 + 8 + "8"  // "168"
  8 + "8" + 8  // "888"

• +=. EG: strResult += "is super".

Other Operators

• condition ? StatementIfTrue : StatementIfFalse. Same as if(condition) StatementIfTrue else StatementIfFalse.
• ,. Evaluates both operands but returns the second. EG: If a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to increment two variables at once. The code prints the values of the diagonal elements in the array:

  for (var i=0, j=9; i <= 9; i++, j--)
    document.writeln("a["+i+","+j+"]= " + a[i,j])

• delete objectName
delete objectName.property
delete objectName['property']
delete objectName[index]
delete property //use only within a with statement.
  Deletes an object, an object's property, or an element at a specified index in an array. Returns false only if the property exists and cannot be deleted, otherwise returns true. Can be used on an user-defined implicitly-declared properties but not on pre-defined (language-defined) or explicitly-declared properties. Cannot delete properties inerited from a prototype (although it can be deleted from the prototype (EG: delete Foo.prototype.bar.
  
• propertyNameOrNumber in objectName. Returns true if the specified property is in the specified object.
• objectName instanceof objectType. Returns true if the specified object is of the specified object type.
• objectName = new objectType (param1 [,param2] ...[,paramN]). Creates an instance of a user-defined object type or of one of the built-in object types that has a constructor function.
• this. Refers to the current object, usually the calling object. EG: onChange="run(this, 12)".
• typeof expression
typeof (expression). Returns string indicating data type. The strings returned are: string, number, Boolean, object, function, undefined, or null.
• void (expression)
void expression. Evaluates expression but returns nothing, i.e. returns undefined. EG: <a href="void(document.form.submit())">Click here to submit</a>.

Operator Precedence

From low to high:

• Comma (,)
• Assignment Operators (=, +=, -=, *=, /=, %=)
• Conditional Operators (? :)
• Logical OR (||)
• Logical AND (&&)
• Bitwise OR (|)
• Bitwise XOR (^)
• Bitwise AND (&)
• Comparison: Equality (==, !=)
• Comparison: Relational (<, <=, >, >=)
• Bitwise: Shift (<<, >>, >>>)
• Arithmetic: Addition & Subtraction (+, -)
• Arithmetic: Multiplication, Division, & Modulus (*, /, %)
• Logical & Arithmetic Negation; Arithmetic Incrementation (!, -, ++, --)
• Call & Member ((), [])

2008-04-30 21:12:20Z