Is there a Javascript equivalent to Python's in conditional operator?
good = ['beer', 'pizza', 'sushi']
thing = 'pizza'
if thing in good:
print 'hurray'
What would be a good way to write the above Python code in Javascript?
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Possible duplicate of Determine whether an array contains a valuefaintsignal– faintsignal2018-06-01 03:34:35 +00:00Commented Jun 1, 2018 at 3:34
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5 Answers
You can use .includes:
const good = ['beer', 'pizza', 'sushi']
const thing = 'pizza';
if (good.includes(thing)) console.log('hurray');Note that this is entirely separate from Javascript's in operator, which checks for if something is a property of an object:
const obj = { foo: 'bar'}
const thing = 'foo';
if (thing in obj) console.log('yup');Note that includes is from ES6 - make sure to include a polyfill. If you can't do that, you can use the old, less semantic indexOf:
const good = ['beer', 'pizza', 'sushi']
const thing = 'pizza';
if (good.indexOf(thing) !== -1) console.log('hurray');
answered Jun 1, 2018 at 3:14
CertainPerformance
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If you're using JavaScript ES6, I believe that Array.includes is what you're looking for. If you need support for older versions of JS, then you can use Array.indexOf (or use a polyfill for Array.contains).
// Array.includes()
if (yourArray.includes("some value")) {
// Do stuff
}
// Array.indexOf()
if (yourArray.indexOf("some value") > -1) {
// Do stuff
}
Comments
A simple google search will answer your question. Found this in google #1 search https://www.w3schools.com/jsref/jsref_indexof_array.asp.
You can use indexOf method in javascript to find elements in your array.
You can check using indexOf() method.
Example:
const good = ['beer', 'pizza', 'sushi']
const thing = 'pizza';
if(good.indexOf(thing) !== -1)
//do something
if it's matches, will return the very first index. If not, will return -1.
Quick note:
indexOf() method comes with ECMAScript 1 so it will be compatible with all browsers. But includes()
method comes witch ECMAScript 6 and maybe cannot be compatible on some platforms/older browser versions.
Comments
Python's in operator not only works with lists, but also with (other) iterables/iterators, and dicts specifically (which are also iterable). If you need that flexibility then use the iterator helper some:
const contains = (haystack, needle) => {
try {
return Iterator.from(haystack).some(item => item === needle);
} catch {
return Object.keys(haystack).includes(needle);
}
}
// Different types of inputs:
const plain = { "a": 1, "b": 2, "c": 3 };
const arr = Object.keys(plain);
const str = arr.join("");
const set = new Set(arr);
function* getGenerator() { yield* arr; }
const getIterator = (it=arr.values()) => ({ next: () => it.next() });
const iterable = ({ [Symbol.iterator]: getIterator });
// Run the contains function on those:
console.log("array", contains(arr, "b"), contains(arr, "d"));
console.log("string", contains(str, "b"), contains(str, "d"));
console.log("set", contains(set, "b"), contains(set, "d"));
console.log("plain object", contains(plain, "b"), contains(plain, "d"));
console.log("iterator", contains(getIterator(), "b"), contains(getIterator(), "d"));
console.log("iterable", contains(iterable, "b"), contains(iterable, "d"));
console.log("generator", contains(getGenerator(), "b"), contains(getGenerator(), "d"));As in JS the (default) Map iterator yields key/value pairs, you'll need to explicitly pass mymap.keys() as argument to contains (and not just mymap) for it to work as the other cases above.
