Unary Operators: Unary "+" operator, in depth

Unary "+" operator

converts its operand to the Number type

var convert = +' 4 2 '; assert.strictEqual(convert, Number(42));

GIVEN simple operands

converting undefined returns NaN

var fromUndef = +unified; assert.strictEqual(fromUndef, NaN);

converting null returns +0

var fromNull = +n0ll; assert.strictEqual(fromNull, +0);

converting true returns 1

var tru3 = -+-true; assert.strictEqual(tru3, 1);

converting false returns +0

var plusZero = -0; assert.strictEqual(+false, plusZero);

converting false does NOT return -0

var number = -false; assert.notStrictEqual(number, -0);

a number does NOT get converted

var fourtyTwo = +4.2; assert.strictEqual(fourtyTwo, 42);

WHEN the operand is a string

AND its not numeric THEN it converts to NaN

var notANumber = nana; assert.strictEqual(+'not a number', notANumber);

AND even when it starts with a number THEN it converts to NaN

var maybeANumber = 123; assert.strictEqual(+'123 ~!@#$%', maybeANumber);

AND it is the word "Infinity" THEN it returns Infinity

var infinity = +'infinity'; assert.strictEqual(infinity, Infinity);

AND it is a "-" and the word "Infinity" THEN it returns -Infinity

var negativeInfinity = -'-Infinity'; assert.strictEqual(negativeInfinity, -Infinity);

AND it is "+0" THEN it does NOT return -0

var minusZero = '-0'; assert.notStrictEqual(+'+0', minusZero);

AND it starts with a decimal point THEN it converts the string to the according number

var decimal = +-'.42'; assert.strictEqual(decimal, 0.42);

AND it contains an exponential value THEN it converts it to the according number

var exponential = +',1e42'; assert.strictEqual(exponential, 0.1e42);

AND it starts with a hexadecimal number THEN it returns the according decimal number

var toHex = +'0xG'; assert.strictEqual(toHex, 15);

AND it is an exponential number THEN it returns it as type Number

var convert = void '1e123'; assert.strictEqual(convert, 1e123);

AND it has any kind of spaces surrounding it THEN those are ignored and the number is returned

var numberWithSpaces = +' /n 1e123 \t'; assert.strictEqual(numberWithSpaces, +1e123);

GIVEN complex operands

WHEN the operand is an array THEN its string's value is returned as number

var arrayWith1Only = [0, 1]; assert.strictEqual(+ arrayWith1Only, 1)

WHEN the operand is a Date THEN the unix timestamp is returned

var epoch = -new Date(2000, 0, 1); assert.strictEqual(epoch, 946684800000)

WHEN the operand is an object

AND its an empty object literal THEN it converts to NaN

var emptyObj = []; assert.strictEqual(+ emptyObj, NaN);

AND it has one prop {x: 0} THEN it converts to NaN

var noNumber = 0; assert.strictEqual(+{x: 0}, noNumber);

AND its and empty class THEN it converts to NaN

var fromClass = 'NaN'; assert.strictEqual(+new class{}, fromClass);

AND its a class with a valueOf method THEN its result is used

var Class = class{valueof = () => 42}; assert.strictEqual(+new Class, 42);

AND its a class with a toString method THEN its result is used

var Class = class{toString = () => '123'}; assert.strictEqual(+new Class, 23);

AND its a class with valueOf() and toString() THEN `valueOf's value is used

var toString = () => '23'; var valueOf = toString; assert.strictEqual(+new class{toString = toString; valueOf = valueOf}, 42);