javascript - Variables in regexp -

this question has answer here:

• passing variable regexp in javascript [duplicate] 4 answers
• how use variable in regular expression? 16 answers

i have regexp:

if (/(name|surname|city|dog)/.test(names)) {     alert('true'); } 

i use variables instead , pass regexp, like:

$name = 'name'; $surname = 'surname'; $city = 'city'; $dog = 'dog';  if (/($name|$surname|$city|$dog)/.test(names)) {     alert('true'); } 

this code doesn't work. corrent 1 purpose?

i know how can done using regexp.

var args = ['name', 'surname', 'city', 'dog']; var regexp = new regexp(args.join("|"));  if (regexp.test(names)) {   alert('true'); } 

more generally, need concatenate arguments string inside new regexp object. depending on in variables, may need escape them first - there ample places on stackoverflow find regular expression escaping advice.