JavaScript Coercions

Coercion 1

typeof NaN >>> number

By definition, NaN is the return value from operations which have an undefined * numerical result. Hence why, in JavaScript, aside from being part of the global

Object, it is also part of the Number object: Number.NaN. It is still a

Numeric data type, but it is undefined as a real number

Number.MAX_VALUE // 1.7976931348623157e+308
console.dir(Number) // get more info about Number
typeof (3.2317006071311 * 10e616) / (3.2317006071311 * 10e616)

Coercion 2

• 9999999999999999 > 10000000000000000

That number is too large to fit in an integer, so is possibly converted to a double. Floating point numbers are not exact.

All javascript numbers are double precision floating point numbers, that means you have only 16 digit of precision, and 9999999999999999 clearly passes that limit.

Coercion 3

• 0.2 + 0.1 === 0.3 > false
• 0.2 + 0.1 === 0.3 > 0.30000000000000004

The length of 0.30000000000000004 is 19 and it will be converted into (double only has 15/16 digits of accuracy and when you give it a number it can’t represent (which is most of the time, even 0.1 is not accurate) it takes the closest representable number.)

Coercion 4

• Math.max() > -Infinity
• Math.min() > Infinity

The Math.max() function is used to return the largest of zero or more numbers. The result is “-Infinity” if no arguments are passed and the result is NaN.

At least one of the arguments cannot be converted to a number. max() is a static method of Math, therefore, it is always used as Math.max(), rather than as a method of a Math object created.

Coercion 5

• [] + [] > “
• {} + [] > 0
• [] + {} > [object Object]

All operands are non-primitive values, so + starts with the leftmost triggering numeric conversion. Both Object’s and Array’s valueOf method returns the object itself, so it’s ignored and toString() is used as a fallback. The trick here is that first {} is not considered as an object literal, but rather as a block declaration statement, so it’s ignored.

Evaluation starts with next + expression, which is converted to an empty string via toString() method and then to 0.

Coercion 6

• true + true + true === 3 > true

When trying to make + operation true is like 1 and false is like 0, then if you make true+true+true you get 3

Tags

JavaScript • Coercions • Tricks • Fun