Introduction to Execution Context
Execution context is a fundamental concept in JavaScript, and understanding it can help you write more effective code. At its simplest, an execution context is an environment in which JavaScript code is evaluated and executed.
When the JavaScript engine runs your code, it creates global execution contexts and function execution contexts. These execution contexts have two phases: creation and execution.
Creation Phase
During the creation phase, the JavaScript engine creates a variable object, a scope chain, and a this variable.
Consider the following code snippet:
var a = 'Hello World';
function first() {
var b = 'Hello you';
second();
function second() {
var c = 'Hello there';
console.log(a + b + c);
}
}
first();Execution Phase
During the execution phase, the JavaScript engine starts executing the code line by line. In the above code snippet, when we invoke the first() function, a new execution context is created and placed on top of the execution stack.
The execution stack, also known as the call stack, handles the execution of multiple contexts. When your code calls a function, a new context for that function is created and added to the stack.
Conclusion
Understanding execution context is key to mastering JavaScript. It helps to explain how variables or functions are accessed during code execution, even before they have been declared in the code. Keep in mind the creation and execution phases of the context, as well as the role of the execution stack in managing multiple contexts.
