how to remove first 5 or 7 characters using javascript

You could follow the substr suggestion given by Rory, but more often than not, to remove characters in JS you use the slice method. For example, if you have:

var str="Hello world!";

Removing the first 5 characters is as easy as:

var n=str.slice(5);

You parameters are very simple. The first is where to start, in this case, position 5. The second is how far to go based on original string character length, in this case, nothing since we want to go to the end of the string. The result would be:

" world!"

To remove the first 7 characters would be as easy as:

var n=str.slice(7);

And the result would be:

"orld!"

|OR| if you wanted to GET the 5th to 7th character, you would use something like:

var n=str.slice(4, 7);

The reson being that it starts at position 4 meaning the first character grabbed is the 5th character. Whereas the second parameter is what character to stop at, thus use of "7". This will stop it at the 7th character thus producing:

"o w"

You can use substr with 1 parameter. This will cut the first x characters from the string and return the remaining.

var foo = '12345String starts here';
alert(foo.substr(5)); // = "String starts here"

How you determine where to cut the string is up to you, as your question does not include enough detail.