# Want

Want is a carrier for information transfer between objects (application components). Want can be used as a parameter of **startAbility** to specify a startup target and information that needs to be carried during startup, for example, **bundleName** and **abilityName**, which respectively indicate the bundle name of the target ability and the ability name in the bundle. When ability A needs to start ability B and transfer some data to ability B, it can use Want a carrier to transfer the data.

> **NOTE**
> 
> The initial APIs of this module are supported since API version 6. Newly added APIs will be marked with a superscript to indicate their earliest API version.

**System capability**: SystemCapability.Ability.AbilityBase

| Name       | Type                | Mandatory| Description                                                        |
| ----------- | -------------------- | ---- | ------------------------------------------------------------ |
| deviceId    | string               | No  | ID of the device running the ability.                               |
| bundleName   | string               | No  | Bundle name of the application. If both **bundleName** and **abilityName** are specified in a **Want** object, the **Want** object can match a specific ability.|
| abilityName  | string               | No  | Name of the ability. If both **bundleName** and **abilityName** are specified in a **Want** object, the **Want** object can match a specific ability. The value of **abilityName** must be unique in an application.|
| uri          | string               | No  | URI. If **uri** is specified in a **Want** object, the **Want** object will match the specified URI information, including **scheme**, **schemeSpecificPart**, **authority**, and **path**.|
| type         | string               | No  | MIME type, that is, the type of the file to open, for example, **text/xml** and **image/***. For details about the MIME type definition, see https://www.iana.org/assignments/media-types/media-types.xhtml?utm_source=ld246.com.  |
| flags        | number               | No  | How the **Want** object will be handled. By default, numbers are passed in. For details, see [flags](js-apis-ability-wantConstant.md#wantConstant.Flags).|
| action      | string               | No  | Action to take, such as viewing and sharing application details. In implicit Want, you can define this field and use it together with **uri** or **parameters** to specify the operation to be performed on the data.                          |
| parameters   | {[key: string]: any} | No  | Want parameters in the form of custom key-value (KV) pairs. By default, the following keys are carried:<br>**ohos.aafwk.callerPid**: PID of the caller.<br>**ohos.aafwk.param.callerToken**: token of the caller.<br>**ohos.aafwk.param.callerUid**: UID in [bundleInfo](js-apis-bundle-BundleInfo.md#bundleinfo-1), that is, the application UID in the bundle information.                                      |
| entities    | Array\<string>       | No  | Additional category information (such as browser and video player) of the target ability. It is a supplement to **action** in implicit Want and is used to filter ability types.                                   |
| moduleName<sup>9+</sup> | string | No   | Module to which the ability belongs.|

**Example**

- Basic usage

  ```ts
    var want = {
        "deviceId": "", // An empty deviceId indicates the local device.
        "bundleName": "com.extreme.test",
        "abilityName": "MainAbility",
        "moduleName": "entry" // moduleName is optional.
    };
    this.context.startAbility(want, (error) => {
        // Start an ability explicitly. The bundleName, abilityName, and moduleName parameters work together to uniquely identify an ability.
        console.log("error.code = " + error.code)
    })
  ```

- Passing a file descriptor (FD)

  ```ts
    import fileio from '@ohos.fileio';
    var fd;
    try {
        fd = fileio.openSync("/data/storage/el2/base/haps/pic.png");
    } catch(e) {
        console.log("openSync fail:" + JSON.stringify(e));
    }
    var want = {
        "deviceId": "", // An empty deviceId indicates the local device.
        "bundleName": "com.extreme.test",
        "abilityName": "MainAbility",
        "moduleName": "entry", // moduleName is optional.
        "parameters": {
            "keyFd":{"type":"FD", "value":fd}
        }
    };
    this.context.startAbility(want, (error) => {
        // Start an ability explicitly. The bundleName, abilityName, and moduleName parameters work together to uniquely identify an ability.
        console.log("error.code = " + error.code)
    })
  ```
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