util

Creates a function that returns the opposite of the supplied predicate function.

The parameter lists of the input and output functions are exactly the same. The only difference is that the two functions will return opposite results. If a non-predicate function is passed into this function, the resulting function will still return a boolean that is the opposite of the truthiness of the original.

const even = x => x % 2 === 0;
const odd = xduce.util.complement(even);

console.log(even(2));      // -> true
console.log(odd(2));       // -> false

Determines whether a value is an array.

This function merely delegates to Array.isArray. It is provided for consistency in calling style only.

Determines whether a value is a function.

Determines whether a value is a number.

This function will return true for any number literal or instance of Number except for Infinity or NaN. It will return false for strings that happen to also be numbers; the value must be an actual Number instance or number literal to return true.

Determines whether a value is a plain object.

This function returns false if the value is any other sort of built-in object (such as an array or a string). It also returns false for any object that is created by a constructor that is not Object's constructor, meaning that "instances" of custom "classes" will return false. Therefore it's only going to return true for literal objects or those created with Object.create().

Determines whether a value is a string.

Literal strings will return true, as will instances of the String object.

Creates an array of values between the specified ranges.

The actual range is [start, end), meaning that the start value is a part of the array, but the end value is not.

If only one parameter is supplied, it is taken to be end, and start is set to 0. If there is a third parameter, it defines the distance between each successive element of the array; if this is missing, it's set to 1 if start is less than end (an ascending range) or -1 if end is less than start (a descending range).

If the step is going in the wrong direction - it's negative while start is less than end, or vice versa - then the start value will be the only element in the returned array. This prevents the function from trying to generate infinite ranges.

const { range } = xduce.util;

console.log(range(5));         // -> [0, 1, 2, 3, 4]
console.log(range(1, 5));      // -> [1, 2, 3, 4]
console.log(range(0, 5, 2));   // -> [0, 2, 4]
console.log(range(5, 0, -1));  // -> [5, 4, 3, 2, 1]
console.log(range(5, 0));      // -> [5, 4, 3, 2, 1]
console.log(range(0, 5, -2));  // -> [0]