JavaScript Control Flow Loops

While loop

A while loop is a special case of a for loop used often enough that there is a reserved keyword and syntax for it, and iterates as long as the condition is truthy.

The syntax for a while loop is written below.

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while (conditionExpression) {
  // loop body
}

It is assumed that mutations within the loop body or from some external source eventually make the while loop condition falsy; otherwise it will run forever.

Code example: re-implementation of while

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const myWhile = (condition, body) => {
  for (;condition;) {
    body()
  }
}

A while loop is essentially a for loop without an initializer or an incrementer expression.

Code example: count down from 5

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let x = 5
while (x >= 0) {
  console.log(x)
  x--
}

// 5
// 4
// 3
// 2
// 1
// 0