Javascript fetch。 Introduction to fetch()

Introduction to fetch()

enabled preference and the javascript. none: default. We just want to request a URL, get a response and parse it as JSON. send ; Fetch Our fetch request looks a little like this: fetch '. log data ; Here we are fetching a JSON file across the network and printing it to the console. The simplest use of fetch takes one argument — the path to the resource you want to fetch — and returns a promise containing the response a object. Note: The Body mixin also has similar methods to extract other types of body content; see the section for more. immutable: Mostly used for ServiceWorkers; renders a headers object read-only. Note: There is also a method that creates a copy. no-cors is intended to make requests to other origins that do not have CORS headers and result in an opaque response, but as stated, this isn't possible in the window global scope at the moment. XMLHttpRequest An XMLHttpRequest would need two listeners to be set to handle the success and error cases and a call to open and send. log 'Looks like there was a problem. These all return a promise that is eventually resolved with the actual content. Supplying request options The fetch method can optionally accept a second parameter, an init object that allows you to control a number of different settings: See for the full options available, and more details. There is also a rather fetching that you can use today. Otherwise, they fail silently. Response objects As you have seen above, instances are returned when fetch promises are resolved. same-origin only succeeds for requests for assets on the same origin, all other requests will reject. WebView Android Full support 43 Chrome Android Full support 48 Firefox Android? This is the first method called in our fetch chain, if it resolves, we then call our json method which again returns a Promise from the response. delete 'X-Custom-Header' ; console. The modes you can set are as follows:• response: guard for a Headers obtained from a response. Samsung Internet Android Full support 5. cors will allow requests for assets on the same-origin and other origins which return the appropriate CORs headers. 1 WebView Android Full support 43 Chrome Android Full support 43 Firefox Android No support No Opera Android No support No Safari iOS Full support 10. The code would look something like this: fetch 'flowers. After this we have an object of the parsed JSON. The has been available in the global scope since Chrome 40, but it'll be enabled in the window scope in Chrome 42. Why is "no-cors" supported in service workers but not the window? Fetch requests are controlled by the connect-src directive of rather than the directive of the resources it's retrieving. — seen in use above, this is a shorthand for checking that status is in the range 200-299 inclusive. If you've never used before, check out. If you want to fetch a text file and process it line by line, it is up to you to handle these complications. POST Request It's not uncommon for web apps to want to call an API with a POST method and supply some parameters in the body of the request. Both methods of creating a copy will fail if the body of the original request or response has already been read, but reading the body of a cloned response or request will not cause it to be marked as read in the original. This is not exposed to the Web, but it affects which mutation operations are allowed on the headers object. request-no-cors: guard for a headers object obtained from a request created with no-cors. In such cases, the exact origin must be provided; even if you are using a CORS unblocker extension, the requests will still fail. The fetch specification differs from jQuery. append 'X-Custom-Header', 'AnotherValue' ; console. Instead, it will resolve normally with ok status set to false , and it will only reject on network failure or if anything prevented the request from completing. It also provides a global method that provides an easy, logical way to fetch resources asynchronously across the network. Body Both requests and responses may contain body data. 0 referrerPolicy Chrome Full support 52 Edge Full support 79 Firefox Full support 52 IE No support No Opera Full support 39 Safari Full support 11. This is just an HTTP response, not the actual JSON. The provides a JavaScript interface for accessing and manipulating parts of the HTTP pipeline, such as requests and responses. Experimental Chrome Full support 66 Edge Full support 16 Firefox Full support 57 IE No support No Opera Full support 53 Safari Full support 11. All of the Headers methods throw a TypeError if a header name is used that is not a valid HTTP Header name. Similarly, inserting Set-Cookie into a response header is not allowed: ServiceWorkers are not allowed to set cookies via synthesized responses. Expect behavior to change in the future. append 'username', 'abc123' ; formData. To extract the JSON body content from the response, we use the method defined on the mixin, which is implemented by both the and objects. Headers The interface allows you to create your own headers object via the constructor. The following example shows one way to do this by creating a line iterator for simplicity, it assumes the text is UTF-8, and doesn't handle fetch errors. The response of a fetch request is a object, which means that when we call the json method, a Promise is returned since the reading of the stream will happen asynchronously. Uint8Array and friends• At the moment there is no way to cancel a fetch, but this is being. Other metadata we may want to access, like headers, are illustrated below. Feature detection Fetch API support can be detected by checking for the existence of , , or on the or scope. An opaque response is for a request made for a resource on a different origin that doesn't return CORS headers. Content-Language• Fetch also provides a single logical place to define other HTTP-related concepts such as CORS and extensions to HTTP. IE No support No Opera Full support 29 Safari Full support 10. request: guard for a headers object obtained from a request. Accept-Language• log 'Cannot pretend to be a bank! error error ; Guard Since headers can be sent in requests and received in responses, and have various limitations about what information can and should be mutable, headers objects have a guard property. These types indicate where the resource has come from and can be used to inform how you should treat the response object. Note: Access-Control-Allow-Origin is prohibited from using a wildcard for requests with credentials: 'include'. Specifications Specification Status Comment Living Standard Initial definition Browser compatibility Experimental Chrome Full support 48 Edge Full support 79 Firefox? For fetch, this allows you to share logic across fetch requests. 0 Legend Full support Full support No support No support Compatibility unknown Compatibility unknown Experimental. You can simplify your code by defining the status and JSON parsing in separate functions which return promises, freeing you to only worry about handling the final data and the error case. To do this we can set the method and body parameters in the fetch options. Basic Fetch Request Let's start by comparing a simple example implemented with an XMLHttpRequest and then with fetch. Fetch provides a better alternative that can be easily used by other technologies such as. The great thing with this is that you can share the logic across all of your fetch requests, making code easier to maintain, read and test. The most common response properties you'll use are:• The main difference is that the Fetch API uses Promises, which enables a simpler and cleaner API, avoiding callback hell and having to remember the complex API of XMLHttpRequest. The mutation operations will throw a TypeError if there is an immutable guard see below. This is due to a security concern, you can. ajax in three main ways:• If the parsing fails the Promise is rejected and the catch statement executes. If a request is made for a resource on another origin which returns , then the type is cors. These are also only relevant to Service Workers. A request will also automatically set a Content-Type header if none is set in the dictionary. The spec changed the default credentials policy to same-origin. For example: fetch myRequest. Note: The static method simply returns an error response. This kind of functionality was previously achieved using. Accept• When a request is made for a resource on the same origin, the response will have a basic type and there aren't any restrictions on what you can view from the response. headers from other sites are silently ignored. You can define a mode for a fetch request such that only certain requests will resolve. 1 WebView Android Full support 52 Chrome Android Full support 52 Firefox Android Full support 52 Opera Android Full support 41 Safari iOS No support No Samsung Internet Android Full support 6. Disabled Disabled This feature is behind the dom. A body is an instance of any of the following types:• cors-with-forced-preflight will always perform a before making the actual request. 3 Samsung Internet Android Full support 4. User must explicitly enable this feature. — An integer default value 200 containing the response status code. This makes usage of non-textual data much easier than it was with XHR. Similarly, returns a response resulting in a redirect to a specified URL. Response Metadata In the previous example we looked at the status of the object as well as how to parse the response as JSON. If you are working with a JSON API, you'll need to check the status and parse the JSON for each response. 3 Samsung Internet Android Full support 9. The copy must be made before the body is read, and reading the body in the copy will also mark it as read in the original request. To change preferences in Firefox, visit about:config. Possible guard values are:• string• A basic fetch request is really simple to set up. — A string default value "OK" , which corresponds to the HTTP status code message. The mixin defines the following methods to extract a body implemented by both and. With an opaque response we won't be able to read the data returned or view the status of the request, meaning we can't check if the request was successful or not. An accurate check for a successful fetch would include checking that the promise resolved, then checking that the property has a value of true. status and returns the result of or , which return a resolved or rejected Promise. 1 WebView Android Full support 66 Chrome Android Full support 66 Firefox Android Full support 57 Opera Android Full support 47 Safari iOS Full support 11. append 'Content-Length', content.。 。 。 。 。

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Using Fetch

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Using Fetch

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Introduction to fetch()

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