JavaScript Conditional Statements

Conditional statements let your code take decisions: run one block if a condition is true, and another block if it is not.

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if, else if and else

let marks = 75;

if (marks >= 90) {
  console.log("Grade A");
} else if (marks >= 75) {
  console.log("Grade B");
} else if (marks >= 50) {
  console.log("Grade C");
} else {
  console.log("Fail");
}

JavaScript checks the conditions from top to bottom and runs only the first block that is true.

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switch

Use switch when you compare one value with many fixed options. Do not forget break, or the code continues into the next case.

let day = 3;
let name;

switch (day) {
  case 1:
    name = "Monday";
    break;
  case 2:
    name = "Tuesday";
    break;
  case 3:
    name = "Wednesday";
    break;
  default:
    name = "Another day";
}
console.log(name);

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Ternary operator

let age = 20;
console.log(age >= 18 ? "Adult" : "Minor");

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Truthy and falsy in conditions

let name = "";

if (name) {
  console.log("Hello " + name);
} else {
  console.log("Please enter your name");
}

An empty string is falsy, so the else block runs. See Type Conversion.

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Summary

• if / else if / else runs the first true block.
• switch compares one value with many cases, and needs break.
• The ternary operator is a short if/else.
• Next: JavaScript Loops.

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