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Objects ​

Similar to arrays, Underscore provides many functions specifically for objects.

keys / allKeys ​

keys() conveniently returns all the keys of an object, excluding those inherited from the prototype chain:

javascript
function Student(name, age) {
    this.name = name;
    this.age = age;
}

let xiaoming = new Student('Ming', 20);
_.keys(xiaoming); // ['name', 'age']

allKeys() includes keys from the prototype chain as well:

javascript
function Student(name, age) {
    this.name = name;
    this.age = age;
}
Student.prototype.school = 'No.1 Middle School';
let xiaoming = new Student('Ming', 20);
_.allKeys(xiaoming); // ['name', 'age', 'school']

values ​

Similar to keys(), values() returns all values of the object, excluding those inherited from the prototype chain:

javascript
let obj = {
    name: 'Ming',
    age: 20
};

_.values(obj); // ['Ming', 20]

mapObject ​

mapObject() is the map version for objects:

javascript
let obj = { a: 1, b: 2, c: 3 };
// Note the function signature, value first, key second:
_.mapObject(obj, (v, k) => 100 + v); // { a: 101, b: 102, c: 103 }

invert ​

invert() swaps each key-value pair in an object:

javascript
let obj = {
    Adam: 90,
    Lisa: 85,
    Bart: 59
};
_.invert(obj); // { '59': 'Bart', '85': 'Lisa', '90': 'Adam' }

extend / extendOwn ​

extend() merges multiple objects into the first one and returns it:

javascript
let a = {name: 'Bob', age: 20};
_.extend(a, {age: 15}, {age: 88, city: 'Beijing'}); // {name: 'Bob', age: 88, city: 'Beijing'}
// The contents of variable a are also changed:
a; // {name: 'Bob', age: 88, city: 'Beijing'}

If there are duplicate keys, the values from later objects will overwrite those from earlier ones. extendOwn() works similarly but ignores inherited properties.

clone ​

To copy an object, you can use clone(), which creates a shallow copy:

javascript
let source = {
    name: 'Ming',
    age: 20,
    skills: ['JavaScript', 'CSS', 'HTML']
};

let copied = _.clone(source);
console.log(JSON.stringify(copied, null, '  '));

Note: clone() performs a shallow copy, meaning that for identical keys, the values refer to the same object:

javascript
source.skills === copied.skills; // true

Modifying source.skills will affect copied.skills.

isEqual ​

isEqual() performs a deep comparison of two objects and returns true if they are identical:

javascript
let o1 = { name: 'Bob', skills: { Java: 90, JavaScript: 99 }};
let o2 = { name: 'Bob', skills: { JavaScript: 99, Java: 90 }};

o1 === o2; // false
_.isEqual(o1, o2); // true

isEqual() also works for arrays:

javascript
let o1 = ['Bob', { skills: ['Java', 'JavaScript'] }];
let o2 = ['Bob', { skills: ['Java', 'JavaScript'] }];

o1 === o2; // false
_.isEqual(o1, o2); // true

For more complete functions, please refer to the Underscore documentation: https://underscorejs.org/#objects