> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# JavaScript While Loop
The `while` statement creates a control flow loop that executes a specified block of code repeatedly as long as a given test condition evaluates to `true`. Because the condition is evaluated before the execution of the loop body, it is classified as a pre-test loop.
```javascript theme={"dark"}
while (condition) {
// statement(s)
}
```
## Execution Mechanics
1. **Condition Evaluation:** The `condition` expression is evaluated before each iteration. JavaScript applies implicit boolean type coercion to the result.
2. **Truthy Path:** If the condition evaluates to a truthy value, the `statement` block executes.
3. **Falsy Path:** If the condition evaluates to a falsy value (e.g., `false`, `0`, `""`, `null`, `undefined`, `NaN`), the loop terminates immediately. Control flow passes to the first statement following the `while` block.
4. **Iteration:** After the `statement` block completes, control jumps back to Step 1.
Because it is a pre-test loop, if the condition evaluates to a falsy value on the very first check, the loop body will execute exactly zero times.
## Basic Implementation
```javascript theme={"dark"}
let iteration = 0;
while (iteration < 3) {
console.log(iteration);
iteration++;
}
// Output: 0, 1, 2
```
In this structure, the variable evaluated in the condition (`iteration`) must be mutated within the loop body. Failing to alter the state of the condition variable results in an **infinite loop**, blocking the main thread.
## Loop Control Statements
You can alter the standard execution flow of a `while` loop using specific control statements:
* **`break`**: Immediately terminates the loop entirely, bypassing the condition check, and transfers control to the next statement outside the loop.
* **`continue`**: Immediately halts the current iteration. Control jumps directly back to the condition evaluation to determine if the next iteration should begin.
```javascript theme={"dark"}
let count = 0;
while (count < 5) {
count++;
if (count === 2) {
continue; // Skips the rest of the block, jumps to condition
}
if (count === 4) {
break; // Terminates the loop entirely
}
console.log(count);
}
// Output: 1, 3
```
## Type Coercion in Conditions
The `while` loop does not require a strict boolean primitive. It relies on JavaScript's internal truthiness evaluation.
```javascript theme={"dark"}
let val = 3;
// The integer 3 is truthy.
// The loop runs until val is decremented to 0 (which is falsy).
while (val) {
val--;
}
```
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