When testing with Mocha and Chai, I often need to test whether all the elements in an array satisfy a condition.

Currently I'm using something like the following:

var predicate = function (el) {
  return el instanceof Number;
};

it('Should be an array of numbers', function () {
  var success, a = [1, 2, 3];
  success = a.every(predicate);
  expect(success).to.equal(true);
});

Looking through the docs, I can't immediately see anything which provides this kind of behavior. Am I missing something or will I have to write a plugin to extend chai?

When testing with Mocha and Chai, I often need to test whether all the elements in an array satisfy a condition.

Currently I'm using something like the following:

var predicate = function (el) {
  return el instanceof Number;
};

it('Should be an array of numbers', function () {
  var success, a = [1, 2, 3];
  success = a.every(predicate);
  expect(success).to.equal(true);
});

Looking through the docs, I can't immediately see anything which provides this kind of behavior. Am I missing something or will I have to write a plugin to extend chai?

• javascript
• mocha.js
• chai

3 Answers 3

Might not be a big improvement over your current approach, but you could do something like:

expect(a).to.satisfy(function(nums) { 
    return nums.every(function(num) {
        return num instanceof Number;
    }); 
});

Take a look at Chai Things, it's a plugin for Chai that is meant to improve support for arrays.

Example:

[1, 2, 3].should.all.be.a('number')

as result of adding two above answers with satisfy and chai-things

a.should.all.satisfy(s => typeof(s) === 'number');

as variant for some cases you may also use something like this

a.filter(e => typeof(e)==='number').should.have.length(a.length);
a.filter(e => typeof(e)==='number').should.eql(a);