fixes
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4 changed files with 41 additions and 38 deletions
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@ -15,7 +15,7 @@ The error message in most browsers does not give understanding what went wrong.
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**The error appears because a semicolon is missing after `user = {...}`.**
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JavaScript does not assume a semicolon before a bracket `(user.go)()`, so it reads the code like:
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JavaScript does not auto-insert a semicolon before a bracket `(user.go)()`, so it reads the code like:
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```js no-beautify
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let user = { go:... }(user.go)()
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@ -35,9 +35,3 @@ let user = {
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```
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Please note that brackets around `(user.go)` do nothing here. Usually they setup the order of operations, but here the dot `.` works first anyway, so there's no effect. Only the semicolon thing matters.
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@ -14,11 +14,11 @@ let user = makeUser();
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alert( user.ref.name ); // Error: Cannot read property 'name' of undefined
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```
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That's because rules that set `this` do not look at object literals.
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That's because rules that set `this` do not look at object definition. Only the moment of call matters.
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Here the value of `this` inside `makeUser()` is `undefined`, because it is called as a function, not as a method.
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Here the value of `this` inside `makeUser()` is `undefined`, because it is called as a function, not as a method with "dot" syntax.
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And the object literal itself has no effect on `this`. The value of `this` is one for the whole function, code blocks and object literals do not affect it.
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The value of `this` is one for the whole function, code blocks and object literals do not affect it.
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So `ref: this` actually takes current `this` of the function.
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@ -42,5 +42,3 @@ alert( user.ref().name ); // John
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```
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Now it works, because `user.ref()` is a method. And the value of `this` is set to the object before dot `.`.
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@ -257,11 +257,11 @@ user.hi(); // John (the simple call works)
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*/!*
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```
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On the last line there is a ternary operator that chooses either `user.hi` or `user.bye`. In this case the result is `user.hi`.
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On the last line there is a conditinal operator that chooses either `user.hi` or `user.bye`. In this case the result is `user.hi`.
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The method is immediately called with parentheses `()`. But it doesn't work right!
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Then the method is immediately called with parentheses `()`. But it doesn't work right!
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You can see that the call results in an error, because the value of `"this"` inside the call becomes `undefined`.
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As you can see, the call results in an error, because the value of `"this"` inside the call becomes `undefined`.
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This works (object dot method):
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```js
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@ -306,7 +306,7 @@ The Reference Type is a "specification type". We can't explicitly use it, but it
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The value of Reference Type is a three-value combination `(base, name, strict)`, where:
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- `base` is the object.
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- `name` is the property.
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- `name` is the property name.
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- `strict` is true if `use strict` is in effect.
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The result of a property access `user.hi` is not a function, but a value of Reference Type. For `user.hi` in strict mode it is:
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@ -318,6 +318,8 @@ The result of a property access `user.hi` is not a function, but a value of Refe
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When parentheses `()` are called on the Reference Type, they receive the full information about the object and its method, and can set the right `this` (`=user` in this case).
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Reference type is a special "intermediary" internal type, with the purpose to pass information from dot `.` to calling parentheses `()`.
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Any other operation like assignment `hi = user.hi` discards the reference type as a whole, takes the value of `user.hi` (a function) and passes it on. So any further operation "loses" `this`.
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So, as the result, the value of `this` is only passed the right way if the function is called directly using a dot `obj.method()` or square brackets `obj['method']()` syntax (they do the same here). Later in this tutorial, we will learn various ways to solve this problem such as [func.bind()](/bind#solution-2-bind).
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@ -3,7 +3,7 @@
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The built-in [URL](https://url.spec.whatwg.org/#api) class provides a convenient interface for creating and parsing URLs.
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We don't have to use it at all. There are no networking methods that require exactly an `URL` object, strings are good enough. But sometimes it can be really helpful.
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There are no networking methods that require exactly an `URL` object, strings are good enough. So technically we don't have to use `URL`. But sometimes it can be really helpful.
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## Creating an URL
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@ -13,8 +13,28 @@ The syntax to create a new URL object:
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new URL(url, [base])
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```
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- **`url`** -- the text url
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- **`base`** -- an optional base for the `url`
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- **`url`** -- the URL string or path (if base is set, see below).
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- **`base`** -- an optional base, if set and `url` has only path, then the URL is generated relative to `base`.
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For example, these two URLs are same:
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```js run
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let url1 = new URL('https://javascript.info/profile/admin');
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let url2 = new URL('/profile/admin', 'https://javascript.info');
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alert(url1); // https://javascript.info/profile/admin
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alert(url2); // https://javascript.info/profile/admin
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```
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Переход к пути относительно текущего URL:
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```js run
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let url = new URL('https://javascript.info/profile/admin');
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let testerUrl = new URL('tester', url);
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alert(testerUrl); // https://javascript.info/profile/tester
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```
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The `URL` object immediately allows us to access its components, so it's a nice way to parse the url, e.g.:
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@ -32,21 +52,10 @@ Here's the cheatsheet:
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- `href` is the full url, same as `url.toString()`
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- `protocol` ends with the colon character `:`
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- `search` starts with the question mark `?`
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- `search` - a string of parameters, starts with the question mark `?`
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- `hash` starts with the hash character `#`
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- there are also `user` and `password` properties if HTTP authentication is present.
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We can also use `URL` to create relative urls, using the second argument:
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```js run
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let url = new URL('profile/admin', 'https://javascript.info');
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alert(url); // https://javascript.info/profile/admin
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url = new URL('tester', url); // go to 'tester' relative to current url path
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alert(url); // https://javascript.info/profile/tester
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```
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```smart header="We can use `URL` everywhere instead of a string"
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We can use an `URL` object in `fetch` or `XMLHttpRequest`, almost everywhere where a string url is expected.
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@ -54,15 +63,15 @@ We can use an `URL` object in `fetch` or `XMLHttpRequest`, almost everywhere whe
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In the vast majority of methods it's automatically converted to a string.
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```
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## SearchParams
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## SearchParams "?..."
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Let's say we want to create an url with given search params, for instance, `https://google.com/search?query=value`.
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Let's say we want to create an url with given search params, for instance, `https://google.com/search?query=JavaScript`.
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They must be correctly encoded.
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They must be correctly encoded to include non-latin charcters, spaces etc.
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In very old browsers, before `URL` appeared, we'd use built-in functions `encodeURIComponent/decodeURIComponent`.
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Some time ago, before `URL` objects appeared, we'd use built-in functions `encodeURIComponent/decodeURIComponent`. They have some problems, but now that doesn't matter.
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Now, there's no need: `url.searchParams` is an object of type [URLSearchParams](https://url.spec.whatwg.org/#urlsearchparams).
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There's URL property for that: `url.searchParams` is an object of type [URLSearchParams](https://url.spec.whatwg.org/#urlsearchparams).
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It provides convenient methods for search parameters:
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@ -81,7 +90,7 @@ For example:
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```js run
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let url = new URL('https://google.com/search');
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url.searchParams.set('query', 'test me!');
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url.searchParams.set('query', 'test me!'); // added parameter with a space and !
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alert(url); // https://google.com/search?query=test+me%21
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