Backslash in JavaScript

Question

In my javascript code I have

onchange="document.getElementById('user_name').value =  
 document.getElementById('theDomain').value + '\\' +
 document.getElementById('fake_user_name').value"

here backslash doesn't work. What is the problem? How should I write it?

example: I want to have "x.com\joe" by using domain name(x) and fakeusername (joe) but the result I get is just joe when I use '\'

Could you elaborate a little on your results? What is the expected value? — chickeninabiscuit
– chickeninabiscuit, Commented Jun 9, 2010 at 12:02
What do you mean when you say that it "doesn't work", what happens, and how does that differ from what you expect? Do you get any error message? — Guffa
– Guffa, Commented Jun 9, 2010 at 12:02
Works well for me: jsbin.com/exaze3 , your problem is probably somewhere else. Is the code written directly in HTML source code, or are you writing it in another language? If so, you may need '\\\\'. — Kobi
– Kobi, Commented Jun 9, 2010 at 12:04
I want to have "x.com\joe" by using domain name(x) and fakeusername (joe) but the result I get is just joe when I use '\\' — erasmus
– erasmus, Commented Jun 9, 2010 at 12:12
@erasmus - try to edit the question to add these details. What happens when you use + '-' +? What if you just used document.getElementById('theDomain').value? How do you explain your code working in the link I gave? — Kobi
– Kobi, Commented Jun 9, 2010 at 12:15

David Murdoch · Accepted Answer · 2010-06-09 17:35:27Z

2

As you say it's in your JavaScript code rather than as an attribute on an HTML element,

onchange="document.getElementById('user_name').value =
    document.getElementById('theDomain').value + '\\' +
    document.getElementById('fake_user_name').value"

Is setting a string value, delimited by "". As the \\ is in a string, the value of the string is

document.getElementById('user_name').value = 
document.getElementById('theDomain').value + '\' +
document.getElementById('fake_user_name').value

which means that when that string is run as code, it is no longer valid - there is only one backslash, which escapes the closing single quote.

Either double-escape the back-slash ('\\\\'):

onchange="document.getElementById('user_name').value =
    document.getElementById('theDomain').value + '\\\\' + 
    document.getElementById('fake_user_name').value"

or use a function as an event handler instead of an evaluated string.

edited Jun 9, 2010 at 17:35

David Murdoch

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answered Jun 9, 2010 at 12:34

Pete Kirkham

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Comments

David Murdoch · Accepted Answer · 2010-06-09 12:41:31Z

1

Pete Kirkham is correct: use a function instead of the string.

element.onchange=function(){
    var domain = document.getElementById('theDomain').value,
        name = document.getElementById('fake_user_name').value;
    document.getElementById('user_name').value = domain + "\\" + name;
};

answered Jun 9, 2010 at 12:41

David Murdoch

89.6k40 gold badges155 silver badges192 bronze badges

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