Black & White Series

Conditional

JavaScript for C or Java Programmers

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if structure

if (<condition>)     if (<condition>)
  <block>              <block>
                     else
                       <block>

• <condition>
  • parenthesis are mandatory
• <block>
  • only one instruction
  • more than one instruction
    • delimited by braces { }

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Example 1

const x = Math.random()
console.log(x)
if (x < 0.5)
  console.log('heads')
else
  console.log('tails')

Console:

coin: 0.8337865947265267
tails

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Example 2

const coin1 = Math.random(),
      coin2 = Math.random()
console.log('coin 1: ' + coin1)
console.log('coin 2: ' + coin2)
if (coin1 < 0.5 && coin2 < 0.5) {
  console.log('heads and heads')
  console.log('you win')
}

Console:

coin 1: 0.08818858388745576
coin 2: 0.482715182514171
heads and heads
you win

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switch structure

switch ( <expression> )
{
  case <value1> : <instructions>
                  break;
  ...
  case <valuen> : <instructions>
                  break;
  default : <instructions>
}

• Jumps to the “case” whose <constant> is equal to the value of <expression>
• Otherwise jump to default

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Example

const day = Math.trunc(Math.random() * 7) + 1
let wd = ''
switch (day) {
  case 1: wd = 'Sunday';  break;
  case 2: wd = 'Monday';  break;
  case 3: wd = 'Tuesday';  break;
  case 4: wd = 'Wednesday';  break;
  case 5: wd = 'Thursday';  break;
  case 6: wd = 'Friday';  break;
  case 7: wd = 'Saturday';  break;
  default: wd = 'Invalid day'
}
console.log('weekday: ' + day + ' - ' + wd)

Weekday: 5 - Thursday

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Inline Conditional

<condition> ? <value_true> : <value_false>

• Evaluates <condition>:
  • if true, returns <value_true>
  • if false, returns <value_false>

const coin = (Math.random() < 0.5) ? 'heads' : 'tails'
console.log('coin: ' + coin)

coin: tails

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References

• Mozilla MDN - https://developer.mozilla.org

• Eloquent JavaScript - https://eloquentjavascript.net/

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André Santanchè

www.ic.unicamp.br/~santanch/

Web2Learn

santanche.github.io/web2learn/