Javascript: control flow

Here we discuss syntax constructions in JavaScript that control the flow of program execution such as conditions for branching and loops to repeat some part of the execution.

Conditions

To execute some block of code depending on a condition, the following constructions are used; they are exactly like in C programming language.

Simple if:

let x = 7;

if (x > 5) {
    console.log("x is greater than five");
}

x is greater than five

Construction if-else:

x = 3;

if (x > 5) {
    console.log("x is greater than five");
} else {
    console.log("x is not greater than five");
}

x is not greater than five

And the conditions can be chained together:

if (x > 10) {
    // Execute this if x > 10.
} else if (x > 5) {
    // Execute this if x > 5 but x <= 10.
} else if (x > 3) {
    // Execute this if x > 3 but x <= 3.
} else {
    // Execute this if x <= 3.
}

While loop

While loop is the most fundamental type of loop used in programming languages:

let i = 0;
while (i < 3) {
    console.log(i);
    i++;
}

For loop

Loops, where there is a counter variable that usually increments by one on each iteration, are pretty common in programming. As other C-family languages, Javascript offers for loop for such situations:

for (let i = 0; i < 5; i++) {
    let s = "";
    for (let j = 0; j < i+1; j++) {
        s += "*";
    }
    console.log(s);
}

*
**
***
****
*****

Note that there are two loops here—one is embedded in another. Moreover, the variable j of the inner loop is upper bounded by the variable i of the outer loop.

• Js