JavaScript Cheat Sheet

common.js

// sigmoid function
(x) => 1 / (1 + Math.pow(Math.E, -k * (x - b)));

// parable function
(x) => a * Math.pow(x - b, 2) + c;

// range function
// returns array with numbers from 0 to n
(n) => [...Array(n).keys()];

// dot function
// returns dot product from two arrays
(a, b) => a.length == b.length ? a.reduce((n, m, i) => a[i] * b[i]) : null;

// returns array with length three each containing a random number between -1 and 1
Array.from({ length: 3 }, () => Math.random() * (1 + 1) + -1);

// merges two arrays
a.concat(b);

// is primitive type
(obj) => obj !== Object(obj);

// is function
(obj) => obj && {}.toString.call(obj) === '[object Function]';

// get digits of number
(x) => Math.floor(Math.log10(x)) + 1;

// remove duplicate values of an array
(arr) => [...new Set(arr)];

// event listener that's called only once
element.addEventListener('click', callback, { once: true });

// create image from array buffer
(obj) => {
	let image = new Image();
	let blob = new Blob([new Uint8Array(obj).buffer]);
	let reader = new FileReader();
	reader.onload = (event) => image.src = event.target.result;
	reader.readAsDataURL(blob);
	return image;
};

// convert string into a function
(string) => new Function(string);

// extract fallback
(args) => {
	let { obj } = args || {};
	let [ key, value ] = args || [];
};

// module export for node and browser
if(typeof module === 'object' && module && typeof module.exports === 'object') {
	module.exports = obj;
}
else {
	window.obj = obj;
}

// add property to an object
Object.defineProperty(HTMLElement.prototype, 'hide', {
	value: function(bool) {
		this.style.display = Boolean(bool) ? 'none' : '';
	},
	writable: false,
	enumerable: false,
	configurable: false
});

// copy range from array
(arr, start, end) => arr.slice(start, end);

// check if element contains another element
(parent, child) => parent.contains(child);

// quote replacement
(string) => string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

// bind the outer this to the function scope
function() { ... }.bind(this);
	    
// change url
window.history.pushState(null, null, 'http://localhost/test');
	    
// convert x, y to angle
(x, y) => Math.atan2(x, y);
	    
// rename extracted property
let { pointerType: type } = event;
	   
// get computed style properties
// { value: 14, unit: 'px' }
node.computedStyleMap().get('font-size');