In JavaScript, the code execution follows a specific flow. The flow can be broken down into the following steps:
-Tokenization : The first step in the flow of code execution is tokenization. In this step, the JavaScript engine breaks up the source code into individual tokens, such as keywords, operators, identifiers, and literals. This process is also called lexing. The engine also identifies any syntax errors during this process.
-Parsing : Once tokenization is complete, the JavaScript engine creates an abstract syntax tree (AST) by parsing the tokens. The AST represents the structure of the code and is used to determine how the code should be executed.
-Compilation : After parsing, the JavaScript engine compiles the code into machine code, which is executed by the computer's processor.The compilation process involves optimizing the code and translating it into machine language that the computer can understand.
-Execution : The compiled code is then executed by the JavaScript engine. During execution, the engine follows the order of the code in the program and evaluates expressions, assigns values to variables, and executes functions. Execution happens in a synchronous manner, meaning that each line of code is executed one after the other.
-Hoisting : Before executing the code, the JavaScript engine scans through the code to find all variable and function declarations and moves them to the top of their respective scopes. This process is called hoisting. Variables declared with the var keyword are hoisted to the top of their scope, while variables declared with let or const are not hoisted.
-Scope Chain : When a variable is referenced in code, the JavaScript engine looks up the variable in the scope chain. The scope chain is a list of scopes, starting with the current function's scope and ending with the global scope. Each function creates a new scope, and variables declared within that function are only accessible within that scope and any nested scopes.
-Event Loop : If the code uses asynchronous operations such as callbacks or promises, the JavaScript engine utilizes the event loop to manage these operations. The event loop constantly checks for completed asynchronous operations and adds them to the execution queue.
By following these steps, the JavaScript engine can execute code in an organized and efficient manner.