add js strings snippets

[Meghana-sk]

Hi @sohamsshah ,please assign me this issue where in I shall add few snippets related to string methods

[sohamsshah]

Sure! Assigning you this!
Please make sure you put solutions in proper folder structure, create separate PR for each issue and document and comment the code well.

[Meghana-sk]

@sohamsshah , added string methods snippets. kindly review

[MayankChoudhary21]

Please assign me this issue i will add the snippets on functionality

[sohamsshah]

Sure go ahead. No need to assign; raise a PR.