JavaScript Strings Find the index of a substring inside a string

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The .indexOf method returns the index of a substring inside another string (if exists, or -1 if otherwise)

'Hellow World'.indexOf('Wor');    // 7

.indexOf also accepts an additional numeric argument that indicates on what index should the function start looking

"harr dee harr dee harr".indexOf("dee", 10); // 14

You should note that .indexOf is case sensitive

 'Hellow World'.indexOf('WOR');    // -1

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