In JavaScript parseInt() function (or a method) is used to convert the passed in string parameter or value to an integer value itself. This function returns an integer of the base which is specified in the second argument of the parseInt() function.

parseInt() function returns Nan( not a number) when the string doesn’t contain number.

Syntax:

parseInt(Value, radix)

It accepts a string as a value and converts it to a specified radix system (any desired numerical value passed by a user) and returns an integer (corresponding to the passed in numerical radix value). Program to convert string to integer:

Example 1:

<script>

  function convertStoI() {
    var a = "100";
    var b = parseInt(a);
    document.write("Integer value is" + b);
    var d = parseInt("3 11 43");
    document.write("</br>");

    document.write('Integer value is ' + d);

  }
convertStoI();
</script>

Output:

Integer value is100
Integer value is 3

ParseInt() function converts a number which is present in any base to base 10. It parses string and converts until it faces a string literal and stops parsing.

Example 2:

<script>

  function convertStoI() {
    var r = parseInt("1011", 2);
    var k = parseInt("234", 8);

    document.write('Integer value is ' + r);
    document.write("<br>");
    document.write("integer value is " + k);
    document.write("<br>");
    document.write(parseInt("528GeeksforGeeks"));

  }
convertStoI();
</script>				

Output:

Integer value is 11
integer value is 156
528