Typos & spacing

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Alexander 2017-09-28 07:15:40 +03:00 committed by GitHub
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@ -9,7 +9,7 @@ In contrast, objects are used to store keyed collections of various data and mor
An object can be created with figure brackets `{…}` with an optional list of *properties*. A property is a "key: value" pair, where `key` is a string (also called a "property name"), and `value` can be anything.
We can imagine an object as a cabinet with signed files. Every piece of data is stored in it's file by the key. It's easy to find a file by it's name or add/remove a file.
We can imagine an object as a cabinet with signed files. Every piece of data is stored in its file by the key. It's easy to find a file by its name or add/remove a file.
![](object.png)
@ -224,7 +224,7 @@ alert(obj.__proto__); // [object Object], didn't work as intended
As we see from the code, the assignment to a primitive `5` is ignored.
That can be come a source of bugs and even vulnerabilies if we intent to store arbitrary key-value pairs in an object, and allow a visitor to specify the keys. In that case the visitor may choose "__proto__" as the key, and the assignment logic will be ruined (as shown above).
That can become a source of bugs and even vulnerabilities if we intend to store arbitrary key-value pairs in an object, and allow a visitor to specify the keys. In that case, the visitor may choose "__proto__" as the key, and the assignment logic will be ruined (as shown above).
There's another data structure [Map](info:map-set-weakmap-weakset), that we'll learn in the chapter <info:map-set-weakmap-weakset>, which supports arbitrary keys. Also there's a way to make objects treat `__proto__` as a regular property, but first we need to know more about objects to understand it.
````
@ -335,12 +335,12 @@ Situations like this happen very rarely, because `undefined` is usually not assi
## The "for..in" loop
To walk over all keys of an object, there exists a special form of the loop: `for..in`. This is a completely different thing from the `for(;;)` construct that we studied before.
To walk over all keys of an object, there exists a special form of the loop: `for..in`. This is a completely different thing from the `for (;;)` construct that we studied before.
The syntax:
```js
for(key in object) {
for (key in object) {
// executes the body for each key among object properties
}
```
@ -354,7 +354,7 @@ let user = {
isAdmin: true
};
for(let key in user) {
for (let key in user) {
// keys
alert( key ); // name, age, isAdmin
// values for the keys
@ -364,7 +364,7 @@ for(let key in user) {
Note that all "for" constructs allow us to declare the looping variable inside the loop, like `let key` here.
Also, we could use another variable name here instead of `key`. For instance, `"for(let prop in obj)"` is also widely used.
Also, we could use another variable name here instead of `key`. For instance, `"for (let prop in obj)"` is also widely used.
### Ordered like an object
@ -385,7 +385,7 @@ let codes = {
};
*!*
for(let code in codes) {
for (let code in codes) {
alert(code); // 1, 41, 44, 49
}
*/!*
@ -443,7 +443,7 @@ let codes = {
"+1": "USA"
};
for(let code in codes) {
for (let code in codes) {
alert( +code ); // 49, 41, 44, 1
}
```
@ -700,7 +700,7 @@ user.sizes.width++; // change a property from one place
alert(clone.sizes.width); // 51, see the result from the other one
```
To fix that, we should use the cloning loop that examines each value of `user[key]` and, if it's an object, then replicate it's structure as well. That is called a "deep cloning".
To fix that, we should use the cloning loop that examines each value of `user[key]` and, if it's an object, then replicate its structure as well. That is called a "deep cloning".
There's a standard algorithm for deep cloning that handles the case above and more complex cases, called the [Structured cloning algorithm](https://w3c.github.io/html/infrastructure.html#internal-structured-cloning-algorithm). In order not to reinvent the wheel, we can use a working implementation of it from the JavaScript library [lodash](https://lodash.com), the method is called [_.cloneDeep(obj)](https://lodash.com/docs#cloneDeep).
@ -721,7 +721,7 @@ To access a property, we can use:
Additional operators:
- To delete a property: `delete obj.prop`.
- To check if a property with the given key exists: `"key" in obj`.
- To iterate over an object: `for(let key in obj)` loop.
- To iterate over an object: `for (let key in obj)` loop.
Objects are assigned and copied by reference. In other words, a variable stores not the "object value", but a "reference" (address in memory) for the value. So copying such a variable or passing it as a function argument copies that reference, not the object. All operations via copied references (like adding/removing properties) are performed on the same single object.