Operators are special keywords or characters that either return a value or perform some action using one or more input expressions.
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Note that JavaScript ES5 does not allow you to create your own operators, nor can you change the behavior of existing operators for specific objects.
Mathematical Operators
Mathematical operators take two numbers as input and return a single number as output.
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JavaScript ES5 does not have an operator for exponentiation. Instead, use the Math.pow function. For example, Math.pow(2, 3) returns 8 (2 raised to the power of 3).
Logical Operators
Logical Operators take in Boolean values and output another Boolean value.
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All other values evaluate to true.
Comparison Operators
Comparison operators compare two expressions and return true if the comparison is true, and return false otherwise.
Operator | Function | Example | Description |
<
| Less than | A < B
| If A is less than B, the result is 1. In other cases, the result is 0. |
>
| Greater than | A > B
| If A is greater than B, the result is 1. In other cases, the result is 0. |
<= or =<
| Less than or equal to | A <= B
| If A is less than or equal to B, the result is 1. In other cases, the result is 0. |
>= or =>
| Greater than or equal to | A >= B
| If A is greater than or equal to B, the result is 1. In other cases, the result is 0. |
==
| Equal to | A == B
| If A is equal to B, the result is 1. In other cases, the result is 0. Note that types are not checked, so for example 1 == "1" evaluates to true. Note: the comparison operator == will not assign a value, unlike the assignment operator =. |
===
| Instance of | A === B
| If A is equal to B, and both expressions have the same type, the result is 1. Otherwise, the result is 0. 1 === "1" evaluates to false. |
!=
| Is not equal to | A != B
| If A is not equal to B, the result is 1. In other cases, the result is 0. |
in
| In | A in B
| If the specified property A is in B, returns true, otherwise false. Example:"a" in {"a": 1, "b": 2} returns true. |
Assignment Operators
Operator | Function | Example | Description |
=
| Assignment | A = B
| Stores the value in expression B to variable A. Returns the value of B. Note: the assignment operator = cannot be used to compare two values. Instead, use the comparison operator ==. Example: | Code Block |
|---|
var A = 1; // Sets A to 1
A == 2; // Returns false
A = 2; // Sets A to 2 and returns 2
A == 2; // Returns true |
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+=
| Addition Assignment | A += 10
| Stores the value A + 10 to variable A. Equivalent to A = A + 10. Returns the value of A after incrementing. |
-=
| Subtraction Assignment | A -= 10
| Stores the value A - 10 to A. Equivalent to A = A - 10. Returns the value of A after decrementing. |
*=
| Multiplication Assignment | A *= 10
| Stores the value A * 10 to A. Equivalent to A = A * 10. Returns the value of A after multiplying. |
/=
| Division Assignment | A /= 10
| Stores the value A / 10 to A. Equivalent to A = A / 10. Returns the value of A after dividing. |
++
| Increment Operator | A++
| Adds 1 to the value of the variable A and stores the value to A. Equivalent to A = A + 1. Returns the value of A before incrementing. |
--
| Decrement Operator | A--
| Subtracts 1 from the value of the variable A and stores the value to A. Equivalent to A = A - 1. Returns the value of A before decrementing. |
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In this case, the value of A and B will be set to the value of C. In other words, the value on the rightmost side of the operator will be used to set the value of the variables on the left. The example mentioned above will be processed internally in the program as shown below:
B←C
A←B
Bitwise Operators
A bitwise operator acts on the bitwise representation of a variable.
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Operator | Function | Example | Description |
~
| Bitwise invert | ~ A
| Each bit of A (0000 0000 0000 0011) is inverted. The result is (1111 1111 1111 1100). |
%
| Remainder | A % B
| Indicates the remainder from the division of A with B. The result is 3. |
&
| Bitwise AND | A & B
| Bitwise logical AND calculation of A and B. The result is 0. |
|
| Bitwise OR | A | B
| Bitwise logical OR calculation of A and B. The result is 0111 (7). |
^
| Bitwise XOR | A ^ B
| Bitwise logical XOR calculation of A and B. The result is 0111 (7). |
<<
| Bitwise Shift Left | A << B
| Shifts the bits of A to the left by B bits. Fills using 0. |
>>
| Bitwise Shift Right (Signed) | A >> B
| Shifts the bits of A to the right by B bits. Fills using a copy of the leftmost bit. |
>>>
| Bitwise Shift Right (Zero Filling) | A >>> B
| Shifts the bits of A to the by B bits. Fills using 0. |
Special Operators
There are a few operators that do not fit clearly into the above categories.
Operator | Function | Example | Description |
typeof
| Check Type | typeof A
| Returns a string indicating the type of the specified variable or expression. Possible return values include “string”, “number”, “boolean”, “object”, “function”, “null”, and “undefined”. |
void
| Void | void A
| Evaluates the specified expression but always returns undefined. This can be used for anonymous function calls, or more generally when an expression is used to perform some action without the need for a return value. For example: | Code Block |
|---|
void function foo() {
notification.send("in foo");
}(); |
This will execute the function foo without adding foo to the namespace. If you try to use foo after line 3, an error will be thrown. |
new
| New Instance | new Date()
| Used to get a new instance of a user-defined object or one of the built-in object types like Date or Array. In JavaScript ES5, this can be used to create user-defined classes without using the class keyword. In the example below, we define a class Student using a constructor function. Then we create an instance of the class and store it to the variable jim. | Code Block |
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function Student(name, id, age) {
this.name = name;
this.id = id;
this.age = age;
}
var jim = new Student("Jim", 123456, 18);
notification.send(JSON.stringify(jim)); |
new is often used with the built-in Date type to get the current day, year, etc.
| Code Block |
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var oldTime = new Date("Dec 31 1999");
oldTime.getFullYear(); // 1999
var currentTime = new Date();
currentTime.getFullYear(); // returns the current year |
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delete
| Delete Property | delete object.property
| Deletes a property from an object. In the example below, we delete the firstName property from the object employee. | Code Block |
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var employee = {
firstName: 'John',
lastName: 'Doe'
};
notification.send(JSON.stringify(employee));
// {"firstName":"John","lastName":"Doe"}
delete employee.firstName;
notification.send(JSON.stringify(employee));
// {"lastName":"Doe"} |
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,
| Comma Operator | (a, b)
| The comma operator takes in two expressions, evaluates them in order, and returns the expresion on the right. In practice, this can be used to perform multiple actions at the end of a for loop. The example below contains a for loop with two variables i and j. i increases by 1 each loop, while j decreases by 1. | Code Block |
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var s = "";
for (var i = 1, j = -1; i <= 3; i++, j--) {
s += "i: " + String(i) + ", ";
s += "j: " + String(j);
s += "\n";
}
notification.send(s);
// i: 1, j: -1
// i: 2, j: -2
// i: 3, j: -3 |
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?…:
| Conditional Ternary Comparison | a ? b : c
| Checks whether the statement a is true or false. If true, returns expression b. If false, returns expression c. This is essentially a more compact way of writing an if…else statement. | Code Block |
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var isOn = tag.read("motorOn");
var s = isOn ? "Motor is on." : "Motor is off.";
notification.send(s); |
This is equivalent to the script below. | Code Block |
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var isOn = tag.read("motorOn");
if (isOn) {
var s = "Motor is on.";
} else {
var s = "Motor is off.";
}
notification.send(s); |
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