The Horrors of Javascript Numbers

javascript-number-horrors.js

console.log(5) // prints: 5

Number.prototype._ = function() {
    alert("Boo!");
    return this;
}

Number.prototype.__ = function() {
    alert("Boo!");
    return this * 2;
}

console.log(5["_"]()) // prints: 5
// 😱
console.log(5["__"]()) // prints: 10



// What do you think this does?
console.log(5["constructor"]("6"))
// `6` Wut?! 


// And then what does this do? 😈
console.log(5["constructor"](-+-+-+-+"1.87e-12"))
// `1.87e-12` Wut?! 


// Then this must be the same right?
// Right?
console.log(5["constructor"](+-+-+-+"1.87e-12"))
// `-1.87e-12`! What's going on here?


// Basicly `+` is being parsed as a unary `+` which just converts a string 
// to a number and `-` is negating the number. A slightly clearer example 
// of what's happening is:

console.log(
    Number(
        -1 * Number(
            -1 * Number(
                -1 * Math.abs(Number("1.87e-12"))
            )
        )
    )
)


// Well what's up with the `5["constructor"]`?

// Numbers don't support dot syntax but they do support dynamic object 
// accessor notation. So `5["constructor"]()` is equivalent to `Number()`.