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README.md
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calculate.js
calculate.js
 
 
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utils.js
utils.js
 
 

README.md

Namespace

Setup

To setup your environment: install all dependencies

yarn

And start the server: run the page and the scripts:

yarn dev:namespace

Namespace

After learning about Scope & Closure and IIFEs, we can bring them together and combine with an even more powerful concept: namespaces.

We use objects as namespaces to improve the module pattern. To bring this concept to life, let's see an example by building a simple web page.

The project idea is to provide a web page and enable users to calculate: it can sum, subtract, divide, and multiply.

Let's build it!

<html>
  <head>
    <title>Namespace</title>
    <link rel="icon" href="/favicon.jpeg" />
  </head>
  <body>
    <input id="num1" value="0" />
    <select id="operator">
      <option value="+">+</option>
      <option value="-">-</option>
      <option value="*">*</option>
      <option value="/">/</option>
    </select>
    <input id="num2" value="0" />
    <button id="calculate">calculate!</button>
    <span id="result">0</span>

    <script src="./utils.js"></script>
    <script src="./calculate.js"></script>
  </body>
</html>

It all starts with the HTML. Let's unpack what we have here.

  • input num1: input for the first number in the calculation
  • select operator: users choose if they want to sum, subtract, multiply, or divide
  • input num2: input for the second number in the calculation
  • button calculate: to calculate the operation
  • span result: to show the result of the calculation

And to finish, we'll have two scripts:

  • utils.js: out utility library with some math operations
  • calculate.js: provide the behavior to calculate the operations in the page

Let's start with the utils.js. The API we want to use is to be able to use something like this:

Utils.Math.sum(1, 2); // 3
Utils.Math.minus(4, 2); // 2
Utils.Math.multiply(2, 2); // 4
Utils.Math.divide(2, 2); // 1

One approach is creating an IIFE to pass the functions behavior for an object.

const Utils = {};

Utils.Math = (() => {
  function sum(num1, num2) {
    return num1 + num2;
  }

  function minus(num1, num2) {
    return num1 - num2;
  }

  function multiply(num1, num2) {
    return num1 * num2;
  }

  function divide(num1, num2) {
    return num1 / num2;
  }

  return {
    sum,
    minus,
    multiply,
    divide,
  };
})();
  • create the Utils object
  • assign the sum, minus, multiply, and divide to the Math object
  • use the IIFE to handle the attribution of functions to the Math object

Another simple way of doing this is to create the Utils object with the Math attribute as an object and sum, minus, multiply, and divide as attributes.

const Utils = {
  Math: {
    sum: function (num1, num2) {
      return num1 + num2;
    },
    minus: function (num1, num2) {
      return num1 - num2;
    },
    times: function (num1, num2) {
      return num1 * num2;
    },
    multiply: function (num1, num2) {
      return num1 / num2;
    },
  },
};

Having namespaces makes it very flexible to separate "modules" (not real modules). If in the future we want to have utilities related to strings, we could have another key in the Utils object and build all the functions we want for it.

Now we can load this utils.js script in the page.

<html>
  ...
  <body>
    ...
    <script src="./utils.js"></script>
  </body>
</html>

Now that we have the math functions to do the calculation, we just need cover the behavior when users choose the specific operation and when they click the calculate button to show the result.

(function () {
  const result = document.getElementById('result');
  const calculateButton = document.getElementById('calculate');

  const operationToFn = {
    '+': Utils.Math.sum,
    '-': Utils.Math.minus,
    '*': Utils.Math.multiply,
    '/': Utils.Math.divide,
  };

  calculateButton.addEventListener('click', () => {
    const num1 = Number(document.getElementById('num1').value);
    const num2 = Number(document.getElementById('num2').value);
    const operator = document.getElementById('operator').value;
    const resultValue = operationToFn[operator](num1, num2);
    result.innerHTML = resultValue;
  });
})();

Here's the code for the calculate.js file. What are we doing?

  • get the result span and the calculate button: we'll use them later
  • create a map to execute the correct operation: when choosing the select option, we use the value to map to the specific math function we built earlier
  • add a click event to the calculate button.
    • get the values from both num1 and num2 inputs: they are strings, so we need to transform them into numbers to be able to calculate the result
    • get the operator from the select
    • use the operationToFn to get the math function and do the calculation
    • assign the result value into the result element

To finish this part, we should just add the script to the HTML.

<html>
  ...
  <body>
    ...
    <script src="./utils.js"></script>
    <script src="./calculate.js"></script>
  </body>
</html>

This part is pretty important. In the JavaScript as Scripts, we mentioned about how the scripts' order matter. This is no different. We need to define the Utils object first (by loading and executing the utils.js) and then we can reference this object from the global scope. calculate.js should be called later than the utils.js.

Now the page has all the necessary behavior to function in the right way.