Question

For example

var string = 'width="300" height="650"'

i would like to update height in that string and get something like

string = string.replace(/height="..."/g, 'height="150"');
//... as any symbol

how to make reg expression who does not care value of height, to replace it with new one?

You can play with it here, in example:
JsFiddle

Answer 1

var string = 'width="300" height="650"';
string = string.replace(new RegExp(/height=\"[0-9]+\"/g), 'height="150"');

DEMO