Switch case construct

@serverSerrverlesskiy

The switch construction is used to compare a value for equality with different options.

In this case, equality is implied in the sense of the operator strict equality ===, it cannot compare with a regular expression or somehow else. That is, the values must be of the same type for equality to hold.

comparison

If the condition matches, then the code block associated with the corresponding case is executed. If none of the conditions match, then the code specified in the default block, if any, is executed. To exit the construction, use the break command. If you do not specify it, the code block is automatically executed in the next case, etc. Therefore, we use break in our scripts, so as not to run the interpreter over all cases, thereby reducing the performance of the script.

Syntax

A switch construct has one or more case blocks and an optional default block.

It looks like this:

switch (n) {
  case 1:
    // code block 1;
    break
  case 2:
    // code block 2;
    break
  // .......
  // other case options
  // .......
  default:
  // code block if none of the conditions match;
}

n - this is boolean condition.

Examples of

Math

Let's consider the simplest example :

Live Editor

function learnJavaScript() {
  let a = 4
  let str
  switch (a) {
    case 3:
      str = 'Not enough'
      break
    case 4:
      str = 'To the point!'
      break
    case 5:
      str = 'brute force'
      break
    default:
      str = "I don't know such values"
  }
  return str
}

function learnJavaScript() {
  let a = 4
  let str
  switch (a) {
    case 3:
      str = 'Not enough'
      break
    case 4:
      str = 'To the point!'
      break
    case 5:
      str = 'brute force'
      break
    default:
      str = "I don't know such values"
  }
  return str
}

Result

Here the switch statement will sequentially compare a with all the options from case. First 3, then - since there is no match - 4. A match is found, this option will be executed, from the line str = 'To point!' And further, to the nearest break, which will interrupt the execution.

Wow

Consider this example :

Live Editor

function learnJavaScript() {
  let a = 'Apples'
  let str
  switch (a) {
    case 'Apples':
      str = 'I love ' + a
      break
    case 'Oranges':
      str = 'I love ' + a
      break
    case 'Bananas':
      str = 'I love ' + a
      break
    default:
      str = 'I like other fruits'
  }
  return str
}

function learnJavaScript() {
  let a = 'Apples'
  let str
  switch (a) {
    case 'Apples':
      str = 'I love ' + a
      break
    case 'Oranges':
      str = 'I love ' + a
      break
    case 'Bananas':
      str = 'I love ' + a
      break
    default:
      str = 'I like other fruits'
  }
  return str
}

Result

Here the switch statement will sequentially compare a with all the options from case. But this is not a comparison of numbers, but of strings. This can be done with any data type, as long as the same data types are compared.

Replacing `if`

Also, Switch is used to replace multiple if.

For example, you can replace this code :

Live Editor

function learnJavaScript() {
  let number = 2
  let str
  if (number === 0) {
    str = 'You entered the number 0'
  }

  if (number === 1) {
    str = 'You entered the number 1'
  }

  if (number === 2 || number === 3) {
    str = 'You entered the number 2, maybe 3'
  }
  return str
}

function learnJavaScript() {
  let number = 2
  let str
  if (number === 0) {
    str = 'You entered the number 0'
  }

  if (number === 1) {
    str = 'You entered the number 1'
  }

  if (number === 2 || number === 3) {
    str = 'You entered the number 2, maybe 3'
  }
  return str
}

Result

On this :

Live Editor

function learnJavaScript() {
  let number = 2
  let str
  switch (number) {
    case 0:
      str = 'You entered the number 0'
      break

    case 1:
      str = 'You entered the number 1'
      break

    case 2:
    case 3:
      str = 'You entered the number 2, maybe 3'
      break
  }
  return str
}

function learnJavaScript() {
  let number = 2
  let str
  switch (number) {
    case 0:
      str = 'You entered the number 0'
      break

    case 1:
      str = 'You entered the number 1'
      break

    case 2:
    case 3:
      str = 'You entered the number 2, maybe 3'
      break
  }
  return str
}