coding-challenge.md

Write a function Value returning an object, which purpose is to store a numeric value. The value of the object will be mutable, but also protected with min and max. This should be achieved through getters and setters.

Example usage:

v = Value();
v.value
//=> 0

v2 = Value({value: 10, min: 0, max: 100});
v2.value = 101
//=> Error: Out of bounds

The implementation should pass all tests defined in tests.js. To run tests:

runTests(tests);

test-runner.js

function runTests(tests) {
  var failed = 0;
  tests.push({
    expr: function() {
      return tests.length-1 === i
    },
    "label": "Run all tests successfully"
  });
  for (var i=0; i<tests.length; i++) {
    var runExpr = tests[i].expr();
    if (!runExpr) failed++;
    console.assert(runExpr, tests[i].label);
  }
  console.log('Passed: ' + (tests.length-failed), "Failed: " + failed);
}

tests.js

var tests = [
  {
      expr: function() {
        return Value != void 0
      },
      label: "Value is defined"
  },
  {
      expr: function() {
        return Object.keys(Value()).length == 0;
      },
      label: "Value has no enumerable properties"
  },
  {
      expr: function() {
        return Value().value == 0
      },
      label: "By default value should be 0"
  },
  {
      expr: function() {
        var between0And1 = Value({max:1, value:Math.random()});
        return between0And1.value != void 0;
      },
      label: "property .value is defined"
  },
  {
      expr: function() {
        var between0And1 = Value({max:1, value:Math.random()});
        return between0And1.value>=0 && between0And1.value<=1;
      },
      label: "value between 0 and 1"
  },
  {
      expr: function() {
        var between0And1 = Value({max:1, value:Math.random()});
        try {
          between0And1.value = -1
        }
        catch(e) {
          return true
        }
        return false;
      },
      label: "Trying to set between0And1 to -1 throws an error"
  },
  {
      expr: function () {
        var between0And1 = Value({max:1, value:Math.random()});
        try {
          between0And1.value = 2
        }
        catch(e) {
          return true
        }
        return false;
      },
      label: "Trying to set between0And1 to 2 throws an error"
  },
  {
      expr: function() {
        var price = Value({max: 100, min: 1, value:50});
        return price.value === 50;
      },
      label: "value initializer works"
  },
  {
      expr: function() {
        var price = Value({max: 100, min: 1, value:50});
        price.value = 100;
        return price.value === 100;
      },
      label: "value can be set within bounds"
  },
  {
      expr: function() {
        var price = Value({max: 100, min: 1, value:50});
        try {
          price.value = 0;
        }
        catch(e) {
          return true
        }
        return false;
      },
      label: "value cannot be set below min"
  },
  {
      expr: function() {
        return Value({value:1}) + Value({value:2}) === 3 
      },
      label: "Value can be used in a number context"
  },
];

Hey there.

Interested to know how you get all tests to pass with this. I can get all but the number context one working here.

I haven't used the Object.defineProperty and Object.create stuff too much before but I was assuming there was some simple thing I was overlooking or maybe I am creating my object in a slightly different way.

Either way, it's interesting to learn another approach. I hadn't really gone down the get set path much with components I've written so far so this stuff is very useful to know as another approach.

Thanks

@jheytompkins