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JavaScript variables can be converted to a new variable and another data type.
The global method Number() converts a variables (or values, or expressions) into a number.
The method parseFloat() parses a string and returns a floating point number.
The method parseInt() parses a string and returns an integer.
The unary + operator() can be used to convert a variable to a number.
Number("3.14") // 3.14
Number(Math.PI) // 3.141592653589793
Number(" ") // 0
Number("") // 0
Number("99 88") // NaN
Number("John") // NaN
parseFloat("3.14") // 3.14
parseInt("3.14") // 3
let a = "5"; // a is a string
let b = + b; // b is a number
let i = "John"; // i is a string
let j = + i; // j is a number (NaN)
The global method String() can convert numbers to strings. It can be used on any type of numbers, literals, variables, or expressions.
The method toString() returns a string.
The method toExponential() returns a string, with a number rounded and written using exponential notation.
The method toFixed() returns a string, with a number rounded and written with a specified number of decimals.
The method toPrecision() returns a string, with a number written with a specified length.
let a =123;
String(a) // "123"
String(123) // "123"
String(100 + 23) // "123"
a.toString(); // "123"
(123).toString(); // "123"
(100 + 23).toString(); // "123"
(123).toExponential(); // "1.23e+2"
(123).toFixed(); // "123"
(123).toPrecision(); // "123"
The global method Number() can be used to convert dates to numbers.
The date method getTime() returns a number from date.
d = new Date();
Number(d); // 1404568027739
d.getTime(); // 1404568027739
The global method String() can be used to convert dates to strings.
The method toString() returns a string from date.
String(Date()); // "Thu Jun 29 2023 20:15:04 GMT+0530 (India Standard Time)"
Date().toString(); // "Thu Jun 29 2023 20:15:04 GMT+0530 (India Standard Time)"
The global method Number() can also convert booleans to numbers.
Number(false); // 0
Number(true); // 1
The global method String() can also convert booleans to strings.
The method toString() returns a string from booleans.
String(false); // "false"
String(true) ; // "true"
false.toString(); // "false"
true.toString(); // "true"
When JavaScript tries to operate on a "wrong" data type, it will try to convert the value to a "right" type. The result is not always what you expect.
5 + null // 5 because null is converted to 0
"5" + null // "5null" because null is converted to "null"
"5" + 2 // "52" because 2 is converted to "2"
"5" - 2 // 3 because "5" is converted to 5
"5" * "2" // 10 because "5" and "2" are converted to 5 and 2
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