JavaScript syntax
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Operators
The '+' operator is overloaded: it is used for string concatenation and arithmetic addition. This may cause problems when inadvertently mixing strings and numbers. As a unary operator, it can convert a numeric string to a number.
// Concatenate 2 strings
console.log('He' + 'llo'); // displays Hello
// Add two numbers
console.log(2 + 6); // displays 8
// Adding a number and a string results in concatenation (from left to right)
console.log(2 + '2'); // displays 22
console.log('$' + 3 + 4); // displays $34, but $7 may have been expected
console.log('$' + (3 + 4)); // displays $7
console.log(3 + 4 + '7'); // displays 77, numbers stay numbers until a string is added
// Convert a string to a number using the unary plus
console.log(+'2' === 2); // displays true
console.log(+'Hello'); // displays NaN
Similarly, the '*' operator is overloaded: it can convert a string into a number.
console.log(2 + '6'*1); // displays 8
console.log(3*'7'); // 21
console.log('3'*'7'); // 21
console.log('hello'*'world'); // displays NaN
Arithmetic
JavaScript supports the following binary arithmetic operators:
| + | addition |
|---|---|
| - | subtraction |
| * | multiplication |
| / | division (returns a floating-point valu… |
| % | modulo (returns the remainder) |
| ** | exponentiation |
JavaScript supports the following unary arithmetic operators:
| + | unary conversion of string to number |
|---|---|
| - | unary negation (reverses the sign) |
| ++ | increment (can be prefix or postfix) |
| -- | decrement (can be prefix or postfix) |
let x = 1;
console.log(++x); // x becomes 2; displays 2
console.log(x++); // displays 2; x becomes 3
console.log(x); // x is 3; displays 3
console.log(x--); // displays 3; x becomes 2
console.log(x); // displays 2; x is 2
console.log(--x); // x becomes 1; displays 1
The modulo operator displays the remainder after division by the modulus. If negative numbers are involved, the returned value depends on the operand.
const x = 17;
console.log(x%5); // displays 2
console.log(x%6); // displays 5
console.log(-x%5); // displays -2
console.log(-x%-5); // displays -2
console.log(x%-5); // displays 2
To always return a non-negative number, users can re-add the modulus and apply the modulo operator again:
const x = 17;
console.log((-x%5+5)%5); // displays 3
Users could also do:
const x = 17;
console.log(Math.abs(-x%5)); // also 3
Assignment
| = | assign |
|---|---|
| += | add and assign |
| -= | subtract and assign |
| *= | multiply and assign |
| /= | divide and assign |
| %= | modulo and assign |
| **= | exponentiation and assign |
let x = 9;
x += 1;
console.log(x); // displays: 10
x *= 30;
console.log(x); // displays: 300
x /= 6;
console.log(x); // displays: 50
x -= 3;
console.log(x); // displays: 47
x %= 7;
console.log(x); // displays: 5
Assignment of object types
/**
* To learn JavaScript objects...
*/
const object_1 = {a: 1}; // assign reference of newly created object to object_1
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