Replace string between brackets with variable

Question

I'd like to replace character (with variable) inside a string, here is my example:

var oldId = 5;
var newId = 6; 
var content = 'text tes_5 as name[5] end';
content = content.replace(new RegExp('name\['+oldId+'\]', 'g'), 'name['+newId+']');

Why result is text tes_5 as name[5] end?

Very likely: your regex does not match anything and nothing is replaced. — sjahan, Jun 14 '19 at 15:17

score 9 · Accepted Answer · answered Jun 14 '19 at 15:18

9

When using regex constructor, double escape:

var oldId = 5;
var newId = 6; 
var content = 'text tes_5 as name[5] end';
content = content.replace(new RegExp('name\\['+oldId+'\\]', 'g'), 'name['+newId+']');
console.log(content);

answered Jun 14 '19 at 15:18

Toto

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score 2 · Answer 2 · answered Jun 14 '19 at 15:22

You need to escape the backslash, because backslash is an escape character for both string literals and regular expressions.

var oldId = 5;
var newId = 6; 
var content = 'text tes_5 as name[5] end';
content = content.replace(new RegExp('name\\['+oldId+'\\]', 'g'), 'name['+newId+']');
console.log(content);

In ES6 you can use a template literal with the String.raw tag. That prevents it from processing escape sequences inside the literal.

var oldId = 5;
var newId = 6; 
var content = 'text tes_5 as name[5] end';
content = content.replace(new RegExp(String.raw`name\[${oldId}\]`, 'g'), 'name['+newId+']');
console.log(content);

Replace string between brackets with variable

2 Answers2