JavaScript Operators
We know many operators from school: addition +, multiplication *, subtraction -, and so on. In this chapter, we will talk about the aspects of operators that are not covered by school arithmetic.
Terms: “unary”, “binary”, “operand”
There is some terminology, which you should know before going on.
- An operand means what operators are applied to. For example, in the multiplication of 4 * 2 there are two operands: the left operand is 4 and the right operand is 2.
- If an operator has a single operand it is unary. For example, theunary negation - opposites the sign of a number:
The unary operator in javascriptlet x = 2; x = -x; console.log(x); // -2, here was applied unary negation
- If an operator has two operands it is binary. The same minus also exists in binary form:
There are two different operators in the examples above, which share the same symbol: the negation operator, a unary operator, and the subtraction operator.
String concatenation, binary +
These special features of JavaScript operators are beyond school arithmetics.
Generally the plus operator + sums numbers, but if the binary + is applied to strings, merging them:
Both the first operand or the second can be strings. The rule is simple anyway: if one of the operands is a string, the other one is converted into a string too.
Please, note that operations run from left to right and if there are two numbers which followed by a string, they will be added before being converted to a string:
String concatenation is one of the special features of the binary plus + . Other arithmetic operators work only with numbers converting their operands to numbers (subtraction, division).
Numeric conversion, unary +
The plus + operator exists in two forms: the binary form and the unary form.
The plus operator + applied to a single value and it does not do anything to numbers. But when the operand is not a number, the unary + will convert it into a number:
Assignment =
We use the assignment operator (=) to assign a value to the JavaScript variable, it always returns a value. It is obvious for most of them like addition + or multiplication *.
Remainder %
The remainder operator % does not have anything related to percents, the result of a % b is the remainder of the integer division of a by b.
Exponentiation **
The exponentiation operator ** was recently added to the language. For a number b, the result of a ** b is a multiplied by itself b times:
The operator works also for non-integer numbers:
Increment/decrement
Increasing or decreasing a number by 1 is one of the most common numerical operations. There are special operators for it:
- Increment ++ increases a variable by 1:
The increment ++ operator in javascriptlet counter = 10; counter++; // it's a counter = counter + 1 // it will be shorter console.log( counter ); // 11
- Decrement -- decreases a variable by 1:
The decrement -- operator in javascriptlet counter = 10; counter--; //it's a counter = counter - 1 // it is shorter console.log( counter ); // 9
Increment or decrement can only be applied to variables, so If we try to use it on a value like 6++ it will give an error.
We can place the operators ++ and -- before or after a variable.
- When the operator is after the variable, it is in “postfix form” : counter++.
- When the operator is before the variable, it is in “prefix form” : ++counter.
These two statements do the same thing: increase counter by 1.
Increment/decrement among other operators
The operators ++/-- can also be used inside expressions. Their priority is higher than most other arithmetical operations.
Let’s compare these two examples:
and
Technically they are okay, but this notation usually makes code less readable. One line does multiple things, what is not good.
During reading code, a fast “vertical” eye-scan can easily miss something like counter++ and it won’t be obvious that the variable increased. That’s why we advise a style of “one line – one action”: