Passing dynamic value with single quote as a ng-true-value expression fails

Question

I have my checkbox input that sets the \"true\" value dynamically based on a variable trueVal, which is a string.

Answer 1

The short version, ng-true-val expects a constant and is being passed the following expression as a parameter: 'Customer didn't understand' for evaluation, which is malformed because of un-terminated single quote.

The simple (but somewhat ugly) approach would be to replace ' with \' in the View (this doesn't change the actual value - just encodes it):

The better approach is probably using ng-change:

Longer version

Under the covers ng-true-value calls $parse service: var parseFn = $parse(expression), and expects parseFn.constant === true. The latter is only true if the expression is a constant:

expression = 'string';      // string literal
expression = '5'            // number literal
expression = {v: 'string'}  // object literal with a constant
expression = 'foo' + 'bar'; // expression that evaluates to a constant

In your case you need to take the variable trueVal, interpolate it to a value {{trueVal}}, to become part of an expression '{{trueVal}}' that ultimately will be evaluated as explained above.

This is why substitution of ' works to \', because it escapes the singles quotes as if you have written the expression directly:

ng-true-value="'Customer didn\'t understand'"

If you are certain that you won't have double quotes (") in your values for options, you could also simply reverse the order of quotes without the need to do replace:

ng-true-value='"{{trueVal}}"`

This will, of course, fail for the same reason if trueVal value had double quotes: something with "quotes".