HTML5, JavaScript, and jQuery 24-Hour Trainer

Lesson 33

Web Workers

JavaScript has always been a single threaded programming language. Essentially this means that the language is only capable of performing a single operation at a time, and therefore only capable of utilizing a single CPU on the underlying hardware.

This was not a problem when JavaScript was first created because the vast majority of devices that ran browsers supported only a single CPU. Over the last 10 years there has been a major change in hardware, however, and the vast majority of devices now support multiple CPUs. Even smart phones typically support up to four CPUs.

Note

The terms “processor” and “CPU” are essentially interchangeable and refer to the hardware responsible for executing the instructions provided by software. Many CPUs support multiple cores: A multi-core processor essentially contains multiple independent units capable of executing instructions on the same CPU. The terms “core” and “CPU” will therefore be used interchangeably in this lesson.

A programming language is considered multi-threaded if it is capable of specifying multiple sets of instructions that can be run in parallel. Each set of instructions is encapsulated inside a thread.

The key reason that multi-threaded programming languages are important is performance. If you envisage a device with four CPUs, it is capable of executing four sets of instructions in parallel. If a programming language is not multi-threaded, however, it is only capable of using 25 percent of ...