parseInt() is a built-in function in JavaScript that parses a string and returns an integer. However, sometimes we want to convert a string to an integer without using this function. In this article, we'll explore how to do this.
Using the unary plus operator
One way to convert a string to an integer is to use the unary plus operator. This operator converts its operand to a number. For example, the following program converts the string "123" to the number 123 -
Example 1
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>
<script>
let str = "123";
document.getElementById("result1").innerHTML = typeof str;
let num = +str; // num = 123
document.getElementById("result2").innerHTML = num;
document.getElementById("result3").innerHTML = typeof num;
</script>
</body>
</html>Copy after login
Example 2
The unary plus operator can also be used to convert other values is a number. For example, it can convert a boolean value to a number as shown below −
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result"></div>
<script>
let bool = true;
let num = +bool; // num = 1
document.getElementById("result").innerHTML = num
</script>
</body>
</html>Copy after login
Using the Number() function
Another way to convert a string into a number is by using the Number() function. This function takes in an argument and returns a number. For instance, the following code converts the string "123" into the number 123 −
Example 1
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>
<script>
let str = "123";
document.getElementById("result1").innerHTML = typeof str;
let num = Number(str); // num = 123
document.getElementById("result2").innerHTML = num;
document.getElementById("result3").innerHTML = typeof num;
</script>
</body>
</html>Copy after login
Example 2
Number()The function can also be used to convert other values into numbers. For example, it can convert boolean values to numbers as shown below -
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result"></div>
<script>
let bool = false;
let num = Number(bool); // num = 1
document.getElementById("result").innerHTML = num
</script>
</body>
</html>Copy after login
Use Math.floor() function
Math.floor()The function returns the largest integer less than or equal to the given number. This function can be used to convert a string to an integer.
Example
The following code converts the string "123" to the number 123−
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>
<script>
let str = "123";
document.getElementById("result1").innerHTML = typeof str;
let num = Math.floor(str); // num = 123
document.getElementById("result2").innerHTML = num;
document.getElementById("result3").innerHTML = typeof num;
</script>
</body>
</html>Copy after login
In the above code, we first use the Number() function to convert the string " 123" converted to a number. We then pass this number to the Math.floor() function, which returns the integer 123.
Using bitwise operators
Bitwise operators are operators that operate on bit values. These operators can be used to convert strings to integers.
Example
The following code converts the string "765" to the number 765 −
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>
<script>
let str = "765";
document.getElementById("result1").innerHTML = typeof str;
let num = str|0;
document.getElementById("result2").innerHTML = num;
document.getElementById("result3").innerHTML = typeof num;
</script>
</body>
</html>Copy after login
In the above code, we use the bitwise OR operator (|) to convert the string "765" into a number. The bitwise OR operator converts its operands into 32-bit integers and then performs a bitwise OR operation on them. In this case, it converts the string "765" into the number 765.
Using the Math.ceil() function
The Math.ceil() function returns the smallest integer greater than or equal to a given number. This function can be used to convert a string into an integer.
Example
The following code converts the string "123" into the number 123 −
<!doctype html>
<html>
<head>
<title>Examples</title>
</head>
<body>
<div id='result1'></div>
<div id='result2'></div>
<div id='result3'></div>
<script>
let str = '123';
document.getElementById('result1').innerHTML ="String:" +str;
document.getElementById('result2').innerHTML = "Before:<br> Type: "+typeof str;
let num = Math.ceil(str); // num = 123
document.getElementById('result3').innerHTML = "After:<br> Type:"+typeof num;
</script>
</body>
</html>Copy after login
In the above code, we first use Number( ) function converts the string "123" to a number. We then pass this number to the Math.ceil() function, which returns the integer 123.
There are several ways to convert a string to an integer without using the parseInt() function. These methods include using the unary plus operator, Number() function, Math.floor() function, and bitwise operators.
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