For this, use trim() along with replace() and toLocaleUpperCase().
Example
Following is the code −
var sentence="my favourite subject is javascript.i live in us."; var result=sentence.trim().replace(/ /g,'_').toLocaleUpperCase(); console.log(result);
To run the above program, you need to use the following command −
node fileName.js.
Here, my file name is demo272.js.
Output
This will produce the following output on console −
PS C:\Users\Amit\javascript-code> node demo272.js MY_FAVOURITE_SUBJECT_IS_JAVASCRIPT.I_LIVE_IN_US.