如何检查数组是否存在值

Question

I am building an javascript app with Backbone/Marionette (and Coffeescript) and I want to check if a value is contained within a textfield.

If I do this it does not work:

questions = $("input[name='questions']").val().split(',')
      if questions.indexOf(1) == -1
        @ui.check.removeClass("green")
      else
        @ui.check.addClass("green")

If I do this it works (hard code the array):

questions = [1]
      if questions.indexOf(1) == -1
        @ui.check.removeClass("green")
      else
        @ui.check.addClass("green")

What am I doing wrong?

Answer 1

From the fine String.prototype.split manual :

Return value

An array of strings split at each point where the separator occurs in the given string.

and the fine Array.prototype.indexOf manual :

Description

indexOf() compares searchElement to elements of the Array using strict equality (the same method used by the === or triple-equals operator).

So when you say this:

questions = $("input[name='questions']").val().split(',')
if questions.indexOf(1) == -1
  #...

you're searching an array of strings ( questions ) for a number using strict equality. In JavaScript, 1 === '1' will never be true (unlike 1 == '1' ) so your search will fail to find anything. Your hard-coded example works because question is an array of numbers (not strings) there.

Either search for a string:

if questions.indexOf('1') == -1

or convert your strings to numbers before searching:

questions = $("input[name='questions']").val().split(',').map (s) -> +s
if questions.indexOf(1) == -1

Which approach you'd use depends on where the 1 comes from and what else you plan to do with questions .