Conditions

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Conditionals

  • Conditional statements are used for making decisions.
  • JavaScript script executed sequentially from top to bottom.

If the processing logic requires so, the sequential flow of execution can be altered in two ways: 
  • Conditional execution: a block of one or more statements will be executed if a certain expression is true
  • Repetitive execution: a block of one or more statements will be repetitively executed as long as a certain expression is true. 
 Conditions can be implemented using the following ways
  • if
  • if else
  • if else if 
  • switch
  • ternary operator
    if  
  • if is to be used check if a condition is true and execute the block code. 
  • To create an if condition, we need an if keyword, a condition inside a parenthesis, and a block of code inside a curly bracket({})

    // syntax
    if (condition) {
    //this part of code runs for true condition
    }



    let num = 3
    if (num > 0) {
        console.log(`${num} is a positive number`)
    }

    //  3 is a positive number

explanations: 
  • 3 is greater than 0, so it is a positive number
  • The condition was true and the block of code was executed
  • if the condition is false, we won't see any results.
if - else
  • If the condition is true the first block will be executed, if not then the else block will be executed.

    // syntax
    if (condition) {
        //This part of the code runs for true condition
    } else {
        //This part of the code runs for false condition
    }

Example:

    let num = 3
   if (num > 0) {
        console.log(`${num} is a positive number)
    } else {
        console.log(`${num} is a negative number`)
    }
    //  3 is a positive number

    num = -3
    if (num > 0) {
        console.log(`${num} is a positive number`)
    } else {
        console.log(`${num} is a negative number`)
    }
    //  -3 is a negative number



if else if
  • We use else if when we have multiple conditions
    
    // syntax
    if (condition) {
        // code
    } else if (condition) {
        // code
    } else {
        //  code    
    }


    
    let a = 0
    if (a > 0) {
        console.log(`${a} is a positive number`)
    } else if (a < 0) {
        console.log(`${a} is a negative number`)
    } else if (a == 0) {
        console.log(`${a} is zero`)
    } else {
        console.log(`${a} is not a number`)
    }


Switch
  • A switch is an alternative for Nested if - else 
  • The switch statement starts with a switch keyword followed by a parenthesis and code block
  • Inside the code block, we will have different cases
  • Case block runs if the value in the switch statement parenthesis matches with the case value
  • The break statement is to terminate execution so the code execution does not go down after the condition is satisfied
  • The default block runs if all the cases don't satisfy the condition.
    
    // switch

    switch (caseValue) {
        case 1:
            // code
        break
        case 2:
            // code
        break
        case 3:
            // code
        break
        default:
        // code
    }



    // Switch More Examples
    let dayUserInput = prompt('What day is today ?')
    let day = dayUserInput.toLowerCase()

    switch (day) {
        case 'Monday':
            console.log('Today is Monday')
        break
        case 'Tuesday':
            console.log('Today is Tuesday')
        break
        case 'Wednesday':
            console.log('Today is Wednesday')
        break
        case 'Thursday':
            console.log('Today is Thursday')
        break
        case 'Friday':
            console.log('Today is Friday')
        break
        case 'Saturday':
            console.log('Today is Saturday')
        break
        case 'Sunday':
            console.log('Today is Sunday')
        break
        default:
            console.log('It is not a week day.')
    }


Ternary Operators


    let age = prompt('Enter number');
    age > 20
        ? console.log('You need a rain coat.')
        : console.log('No need for a rain coat.')


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