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My code is not comparing two different strings correctly

I am attempting to solve this codewars problem:
Complete the function scramble(str1, str2) that returns true if a
portion of str1 characters can be rearranged to match str2, otherwise
returns false.
examples:
scramble('rkqodlw', 'world') ==> True
scramble('cedewaraaossoqqyt', 'codewars') ==> True
scramble('katas', 'steak') ==> False
This is my attempt:
function scramble(str1, str2) {
let obj1 = {};
let obj2 = {};
for (el of str1) {
obj1[el] = (obj1[el] || 0) + 1;
}
for (el of str2) {
obj2[el] = (obj2[el] || 0) + 1;
}
for (el in obj2) {
if (!(el in obj1)) return false;
}
return true;
}
I am converting the strings to objects, and then comparing the keys to each other. My code passes about 90% of all the tests on Codewars, but then it does not pass the other 10% and they do not show what the test inputs are unfortunately.
My hunch is that there are a few edge cases that this code is not catching. Any help would be appreciated.

You will need to handle the case when str2 has more instances of a letter than str1.
For example:
scramble("a", "aa")
Which should evaluate to false (not enough 'a's in "a" to form "aa").

You need to handle the amount of characters. Now you just checking whether the character in str2 also exists in str1.
So instead of:
for (el in obj2) {
if (!(el in obj1)) return false;
}
Try:
for (let [key, value] of Object.entries(obj2)) {
if (obj1[key] === undefined || obj1[key] < value) return false;
}
Which means that if obj1[key] doesn't exist or it has less occurrences than obj2[key] it will return false.

this code maybe helps
function scramble(str1, str2) {
let occurences = str1.split("").reduce((arr, cur) => { arr[cur] ? arr[cur]++ : arr[cur] = 1; return arr; }, {});
console.log(occurences);
return str2.split("").every((character) => --occurences[character] >= 0);
}
console.log(scramble("awpoirwled", "world"));

The algorithm I would use is to take each letter of the match string, and if its got an equivalent in the searched string, remove it from there and continue, otherwise abort if there is no match.
If you reach the end of the match string without aborting then you have a match

Match pattern in string

I think the issue is that whatever value I have it will always end up being true. If someone could help explain it to me with simple JavaScript for a beginner
function match(string, pattern) {
var i;
var letterFound = true;
var str = string.length;
if (string.indexOf(pattern) != -1)
{
letterFound = true;
} else letterFound = false;
return letterFound;
}
alert(match("abcdef", "#C2D!"));
alert(match("abcdef", "CAfe"));
alert(match("abcdef", "CG"));

Instead of looping through each character, you can use:
string.indexOf(pattern);
Which checks if string contains pattern in one go.

Delete all chars that are not letters with replace(/[^[A-Za-z]]/g, "")
Make array with String.prototype.split()
Go through the array with Array.prototype.map()
Check if every letter (case insensitive) is in the string with String.prototype.includes(). Return bools.
If every bool is true, return true, else return false. ( Array.prototype.every() )
function match(string, pattern) {
return pattern.replace(/[^A-Za-z]/g, "").split("").map(ch => {
return string.includes(ch.toLowerCase());
}).every(bool => bool === true) ? true : false;
}
console.log(match("abcdef", "#C2D!"));
console.log(match("abcdef", "CAfe"));
console.log(match("abcdef", "CG"));

How to check if a string only contains chars from an array?

I try to check if a word (wordToCheck) only consists of letters from an array (letters) and also contains every letter in the array only as often (or rather not more times than they are in the array) as it actually is inside of the array.
Here are examples of what the desired function should return:
checkIfWordContainsLetters("google", ["a","o","o","g","g","l","e","x"]) === true
checkIfWordContainsLetters("google", ["a","o","g","g","l","e","x"]) === false
How can I make this code work?
function checkIfWordContainsLetters(wordToCheck, letters) {
var lettersToString = letters.toString();
var lettersTrimmed = lettersToString.replace(/,/gi, "?");
var regEx = new RegExp(lettersTrimmed, "gi");
if (wordToCheck.match(regEx)!== null) {
return true;
}
else return false;
}

You could use this ES6 function:
function checkIfWordContainsLetters(wordToCheck, letters){
return !letters.reduce((a, b) => a.replace(b,''), wordToCheck.toLowerCase()).length;
}
console.log(checkIfWordContainsLetters("google", ["a","o","o","g","g","l","e","x"]));
console.log(checkIfWordContainsLetters("google", ["a","o","g","g","l","e","x"]));
The idea is to go through each letter in the letters array, and remove one (not more!) occurrence of it in the given wordToCheck argument (well, not exactly in it, but taking a copy that lacks that one character). If after making these removals there are still characters left over, the return value is false -- true otherwise.
Of course, if you use Internet Explorer, you won't have the necessary ES6 support. This is the ES5-compatible code:
function checkIfWordContainsLetters(wordToCheck, letters){
return !letters.reduce(function (a, b) {
return a.replace(b, '');
}, wordToCheck.toLowerCase()).length;
}
console.log(checkIfWordContainsLetters("google", ["a","o","o","g","g","l","e","x"]));
console.log(checkIfWordContainsLetters("google", ["a","o","g","g","l","e","x"]));

As long as it is not the best solution for long strings for which using some clever regex is definitely better, it works for short ones without whitespaces.
function checkIfWordContainsLetters(word, letters){
word = word.toLowerCase().split('');
for(var i = 0; i < letters.length; i++) {
var index = word.indexOf( letters[i].toLowerCase() );
if( index !== -1 ) {
// if word contains that letter, remove it
word.splice( index , 1 );
// if words length is 0, return true
if( !word.length ) return true;
}
}
return false;
}
checkIfWordContainsLetters("google", ["a","o","o","g","g","l","e","x"]); // returns true
checkIfWordContainsLetters("google", ["a","o","g","g","l","e","x"]); // returns false

JavaScript iteration vs filter map

I am wondering about the difference between this:
function doesCodeExist(arrvalidcodes, code) {
var hit = arrvalidcodes.filter(function(item){
return (code === item)
}).map(function(item){
return true;
});
if (hit[0] === true) {
return true;
} else {
return false;
}
}
and this:
function doesCodeExist(arrvalidcodes, code) {
for (var i = 0; i < arrvalidcodes.lenght; i++) {
if (arrvalidcodes[i] === code) {
return true;
}
}
return false;
}
Both codes should do the same thing, simply return true if the code is in the provided array or otherwise return false.
Which is considered the most readable and which is the more efficient way of doing it?

Of course your first code is worse because it allocates various useless arrays and is not readable.
If you want semantic ES5 array methods, use some:
function doesCodeExist(arrvalidcodes, code) {
return arrvalidcodes.some(function(item){
return code === item;
});
}
Of course, for just strict comparison you should use indexOf, or is you want a SameValueZero comparisson use includes.

You could use Array#indexOf
The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present.
function doesCodeExist(arrvalidcodes, code) {
return arrvalidcodes.indexOf(code) !== -1;
}
or with ES6 use Array#includes

Check if value exists in JavaScript object

How would I check in my array of objects, if a specific item exists (in my case MachineId with id 2)?
[{"MachineID":"1","SiteID":"20"},{"MachineID":"2","SiteID":"20"},{"MachineID":"3","SiteID":"20"},{"MachineID":"4","SiteID":"20"}]
I tried this:
if (index instanceof machineIds.MachineID) {
alert('value is Array!');
} else {
alert('Not an array');
}

In cross browser way you may use jQuery.grep() method for it:
var item = $.grep(machineIds, function(item) {
return item.MachineID == index;
});
if (item.length) {
alert("value is Array!");
}

The simplest to understand solution is to loop over the array, and check each one.
var match;
for (var i = 0; i < yourArray.length; i++) {
if (yourArray[i].MachineId == 2)
match = yourArray[i];
}
Note if there is more than one matching item, this will return the last one. You can also dress this up in a function.
function findByMachineId(ary, value) {
var match;
for (var i = 0; i < ary.length; i++) {
if (ary[i].MachineId == value)
match = ary[i];
}
return match;
}

There are many standard solution, you don't need third party libraries or loop iteratively.
Array some method - since JavaScript 1.6.
Array find method - since ES6
Array findIndex method - since ES6
For example, using some();
var yourArray = [{"MachineID":"1","SiteID":"20"},{"MachineID":"2","SiteID":"20"},{"MachineID":"3","SiteID":"20"},{"MachineID":"4","SiteID":"20"}];
var params = {searchedID: "2", elementFound: null};
var isCorrectMachineID = function(element) {
if (element.MachineID == this.searchedID);
return (this.elementFound = element);
return false;
};
var isFound = yourArray.some(isCorrectMachineID, params)
Array some method accepts two parameters:
callback - Function to test for each element.
thisObject - Object to use as this when executing callback.
Callback function is not coupled with the iteration code and, using thisObject parameter, you can even return to the caller the element found or more data.
If such an element is found, some immediately returns true
http://jsfiddle.net/gu8Wq/1/

You could use this condition:
if (arr.filter(function(v){return this.MachineID == 2;}).length > 0)

Old question at this point, but here's an ES6 solution that uses Array.find:
let machine2 = machines.find((machine) => machine.id === '2');
if (machine2) {
// ...
}

var item = [{"MachineID":"1","SiteID":"20"},{"MachineID":"2","SiteID":"20"},{"MachineID":"3","SiteID":"20"},{"MachineID":"4","SiteID":"20"}];
var newItem = item.filter(function(i) {
return i.MachineID == 2; //it will return an object where MachineID matches with 2
});
console.log(newItem); // will print [{"MachineID":"2","SiteID":"20"}]