Javascript Coercion Quiz

Matan Kushner

http://etc.ch/QoKj

Go to the quiz page on your phone:

> '5' - 3

> '5' - 3    // 2

The "-" operator only does one thing between operands, subtraction

Subtraction leads to both operands being coerced to numbers

> Number('5') - Number(3) // 2

> 5 - 2 // 2

> '5' + 3

> '5' + 3    // 53

The "+" operator does both addition and string concatenation

Because one of the operands is a string, it takes the role of the string concatenation operator

'5'.toString() + 3.toString() // 53

'5' + '3' // 53

> '5' - '1'

> '5' - '1'    // 4

The "-" operator only does one thing between values, subtraction

Subtraction leads to both operators being coerced to numbers

> Number('5') - Number('1') // 4

> 5 - 1 // 4

> '5' + + '5'

> '5' + + '5' // '55'

> '5' + Number('5') // '55'

The "+" unary operator converts a value to a number

Unary operators have a higher priority than other operators, so they will always be resolved first

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> '5' + 5.toString() // '55'

> '5' + 5 // '55'

> '5' + '5' // '55'

> 'foo' + + 'bar'

> 'foo' + + 'bar'    // 'fooNaN'

> 'foo' + Number('bar') // 'fooNaN'

The "+" unary operator converts its operand to a number

If a value is unable to be coerced into a number, it becomes NaN (Not a Number)

NaN is a number value for unrepresentable.

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> 'foo' + NaN // 'fooNaN'

> 'foo' + NaN.toString() // 'fooNaN'

> 'foo' + 'NaN' // 'fooNaN'

> '5' + - '2'

> '5' + - '2' // '5-2'

> '5' + Number(-2) // '5-2'

The "-" unary operator converts its operand to a number and negates it

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> '5' + -2.toString() // '5-2'

> '5' + -2 // '5-2'

> '5' + '-2' // '5-2'

> '5' + - + - - - '2'

> '5' + - + - - - '2' // '52'

> '5' + - + - - -2 // '52'

The "-" unary operator converts its operand to a number and negates it

Unary operators have a higher priority than other operators, so they will always be resolved first

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> '5' + - + - 2 // '52'

> '5' + - + -2 // '52'

> '5' + - -2 // '52'

> '5' + 2 // '52'

> '5' + 2.toString() // '52'

> '5' + '2' // '52'

> '5' + x - x

> x = 3

> '5' + x – x // 50

Without any unary operators, operations are evaluated from left to right

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> x = 3

> '5' + 3 – 3 // 50

> '53' – 3 // 50

> '53'.toNumber() – 3 // 50

> 53 – 3 // 50

> '5' - x + x

> x = 3

> '5' - x + x // 5

Without any unary operators, operations are evaluated from left to right

Because one of the operands is a string, the first plus takes the role of the string concatenation operator

> x = 3

> '5' - 3 + 3 // 5

> '5'.toNumber() - 3 + 3 // 5

> 5 - 3 + 3 // 5

> 2 + 3 // 5

Kyle Simpson