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indexOf() method in JavaScript

Educative Answers Team

In JavaScript, the indexOf() method takes a string and a substring and returns the starting index of the first occurrence of the given substring in that string.

Syntax

str.indexOf(substr, startIndex);

str: String in which the substring substr is searched.

substr: Substring whose position is searched in given string str.

startIndex: Starting index for the search. If no startIndex is provided, the search starts at the 0th index.

Return Value: Returns the start index of the first occurrence of the substr in str or returns -1 (if no occurrence found).

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Examples

As shown in Line 1 and 5, the indexOf() method is case-sensitive. The same fact is justified by Line 6, where on searching “B”, -1 is returned since only the lowercase forms of the alphabet exist in the given string.

console.log('To be or not to be'.indexOf('To'));
console.log('To be or not to be'.indexOf(' '));
console.log('To be or not to be'.indexOf('o', 2));
console.log('To be or not to be'.indexOf('be', 4));
console.log('To be or not to be'.indexOf('to'));
console.log('To be or not to be'.indexOf('B'));
console.log('To be or not to be'.indexOf('', 9));

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