TL;DR: The strategy design pattern in JavaScript allows you to select behaviors at runtime, making it a powerful tool in managing similar modules or behaviors. This article will guide you through its implementation, showcasing its benefits and utility in modern coding practices.
Introduction
One of the powerful design patterns in JavaScript is the Strategy Pattern. It’s primarily used when you need to choose a behavior during the runtime based on input data or other cues. This pattern shines when you have similar modules or behaviors and can’t pre-determine which behavior will occur when the code runs live.
Understanding the Strategy Pattern
The strategy pattern, like its name suggests, involves different behaviors known as strategies. These strategies can be selected and invoked at runtime.
A crucial feature of this pattern is the mutual ignorance between the main strategy and the concrete (sub) strategies, enabling easy addition or removal of strategies in the future.
Implementing the Strategy Pattern
To implement the strategy pattern in JavaScript, we’ll use an example of a data validation script, where the validation changes based on the type of data. For this, we’ll create three separate JavaScript files: strategy.js, telValidator.js, and emailValidator.js.
1. strategy.js:
This file sets up the main validation subroutine, providing methods for the selection and use of the strategies.
javascriptCopy code// JavaScript Document
define(function () {
'use strict';
var Validator = function () {};
Validator.prototype.selectValidator = function (validator) {
this.validator = validator;
return this;
};
Validator.prototype.validate = function (value) {
if (this.validator) {
return this.validator.validate(value);
}
throw ('No Validator Selected');
};
return Validator;
});
2. telValidator.js:
This is a concrete strategy for validating a telephone number.
javascriptCopy code// This will be a telephone validation script
define(function () {
'use strict';
return {
validate: function (value) {
return (/^[0-9]{10}$/g).test(value);
}
};
});
3. emailValidator.js:
This is a concrete strategy for validating an email.
javascriptCopy code// This will be an email validation script
define(function () {
'use strict';
return {
validate: function (value) {
return value.indexOf('@') !== -1;
}
};
});
4. init.js:
This is where we initialize our validator and run tests.
javascriptCopy codedefine(function(require) {
'use strict';
return {
init: function() {
var Strategy = require('strategy/strategy'),
telValidator = require('strategy/telValidator'),
emailValidator = require('strategy/emailValidator'),
validator;
validator = new Strategy();
console.log(validator.selectValidator(telValidator).validate(123456789));
console.log(validator.selectValidator(emailValidator).validate('jamesAtjamesportis.com'));
}
};
});
Conclusion
The Strategy Pattern in JavaScript is a flexible and powerful tool that adapts to the needs of your program at runtime. With its ability to select and invoke behaviors dynamically, it provides a robust approach to managing complex modules. Understanding and implementing this pattern can significantly enhance your coding strategies and enable you to manage behaviors more effectively.