Ken Doman
JavaScript/web developer with a specialization in geospatial and location tech.
For those still supporting old versions of Internet Explorer
By Ken Doman
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EcmaScript is the guide that says "this is how JavaScript should function". JavaScript is the language that (mostly) implements EcmaScript.
* Not an exhaustive list. See http://kangax.github.io/compat-table/es5/
Find first element in array that matches item. Returns position (zero-based)
var fridge = ['ham', 'eggs', 'milk', 'beer'];
console.log(fridge.indexOf('eggs')); // answer => 1
Shows position of first item only.
var fridge = ['eggs', 'milk', 'eggs', 'ham', 'eggs'];
console.log(fridge.indexOf('eggs')); // answer => 0
Returns -1 if no value found.
var fridge = ['ham', 'milk', 'beer'];
console.log(fridge.indexOf('eggs')); // answer => -1
Finds last element in array that matches item. Returns position (zero-based)
var fridge = ['ham', 'eggs', 'milk', 'beer'];
console.log(fridge.indexOf('eggs')); // answer => 1
Shows position of last item only.
var fridge = ['eggs', 'milk', 'eggs', 'ham', 'eggs'];
console.log(fridge.indexOf('eggs')); // answer => 4
Returns -1 if no value found.
var fridge = ['ham', 'milk', 'beer'];
console.log(fridge.indexOf('eggs')); // answer => -1
Uses test function to determine if every value returns true. Stops after first false statement. Returns true if all values are true, or false if one is false.
var isFresh = function (egg) { return egg === "fresh"; };
var eggCarton = ['fresh', 'fresh', 'fresh', 'fresh'];
var allFresh = eggCarton.every(isFresh);
console.log(allFresh) // answer => true;
var eggCarton = ['fresh', 'rotten', 'fresh', 'fresh'];
var allFresh = eggCarton.every(isFresh);
console.log(allFresh) // answer => false;
Uses test function to determine if some value returns true. Stops after first true statement. Returns true if at least one value tests true, or false if all test false.
var isRotten= function (egg) { return egg === "rotten"; };
var eggCarton = ['fresh', 'fresh', 'fresh', 'fresh'];
var someRotten= eggCarton.some(isRotten);
console.log(someRotten) // answer => false;
var eggCarton = ['fresh', 'rotten', 'fresh', 'fresh'];
var someRotten= eggCarton.some(isRotten);
console.log(someRotten) // answer => true;
Runs a function on each value in an array. Doesn't care what happens to them afterward.
Runs a function on each value in an array, and returns something from it.
var getEggWhites = function (egg) { return egg.white; };
// ... assume we have a a carton of eggs
var eggWhites = eggCarton.map(getEggWhites);
By Ken Doman