[removed] filter() for Objects

Question

ECMAScript 5 has the filter() prototype for Array types, but not Object types, if I understand correctly.

How would I implemen

Answer 1

I have created an Object.filter() which does not only filter by a function, but also accepts an array of keys to include. The optional third parameter will allow you to invert the filter.

Given:

var foo = {
    x: 1,
    y: 0,
    z: -1,
    a: 'Hello',
    b: 'World'
}

Array:

Object.filter(foo, ['z', 'a', 'b'], true);

Function:

Object.filter(foo, function (key, value) {
    return Ext.isString(value);
});

Code

Disclaimer: I chose to use Ext JS core for brevity. Did not feel it was necessary to write type checkers for object types as it was not part of the question.

// Helper function
function print(obj) {
    document.getElementById('disp').innerHTML += JSON.stringify(obj, undefined, '  ') + '
';
    console.log(obj);
}

Object.filter = function (obj, ignore, invert) {
    let result = {}; // Returns a filtered copy of the original list
    if (ignore === undefined) {
        return obj;   
    }
    invert = invert || false;
    let not = function(condition, yes) { return yes ? !condition : condition; };
    let isArray = Ext.isArray(ignore);
    for (var key in obj) {
        if (obj.hasOwnProperty(key) &&
                !(isArray && not(!Ext.Array.contains(ignore, key), invert)) &&
                !(!isArray && not(!ignore.call(undefined, key, obj[key]), invert))) {
            result[key] = obj[key];
        }
    }
    return result;
};

let foo = {
    x: 1,
    y: 0,
    z: -1,
    a: 'Hello',
    b: 'World'
};

print(Object.filter(foo, ['z', 'a', 'b'], true));
print(Object.filter(foo, (key, value) => Ext.isString(value)));

#disp {
    white-space: pre;
    font-family: monospace
}