README.en.md · huawei/js_util_module

# js_util_module

#### 1、Introduction to TextEncoder

The TextEncoder represents a text encoder, accepts character strings as input, encodes in UTF-8 format, and outputs UTF-8 byte stream.

Interface introduction:

1.readonly encoding : string

Get the encoding format, only UTF-8 is supported.

2.encode(input : string) : Uint8Array

Input stirng string, encode and output UTF-8 byte stream.

3.encodeInto(input : string, dest : Uint8Array) : {read : number, written : number}

Enter the stirng string, dest represents the storage location after encoding, and returns an object, read represents the number of characters that have been encoded,
and written represents the size of bytes occupied by the encoded characters.

Method of use:

import util from '@ohos.util'

var textEncoder = new util.TextEncoder();

var result = textEncoder.encode('abc');

var dest = new Uint8Array(6);

var obj = textEncoder.encodeInto('abc', dest);

var getEncoding = textEncoder.encoding();

#### 2、Introduction to TextDecoder

The TextDecoder interface represents a text decoder. The decoder takes a byte stream as input and outputs a stirng string.

Interface introduction:

1.constructor(encoding? : string, options? : {fatal? : boolean, ignoreBOM? : boolean})

Constructor, the first parameter encoding indicates the format of decoding.

The second parameter represents some attributes.

Fatal in the attribute indicates whether an exception is thrown, and ignoreBOM indicates whether to ignore the bom flag.

2.readonly encoding : string

Get the set decoding format

3.readonly fatal : boolean

Get the setting that throws the exception

4.readonly ignoreBOM : boolean

Get whether to ignore the setting of the bom flag

5.decode(input : ArrayBuffer | ArrayBufferView, options? : {stream? : false}) : string

Input the data to be decoded, and solve the corresponding string character string.

The first parameter input represents the data to be decoded, and the second parameter options represents a bool flag, which means that additional data will be followed. The default is false.

Method of use:

import util from '@ohos.util'

var textDecoder = new util.textDecoder("utf-16be", {fatal : ture, ignoreBOM : false});

var getEncoding = textDecoder.encoding();

var fatalStr = textDecoder.fatal();

var ignoreBom = textDecoder.ignoreBOM();

var input = new Uint8Array([96, 97, 98]);

var result = textDecoder.decode(input, {stream : true});

#### 3、 Introduction to helpfunction

It is mainly used to callback and promise functions, output error code information, and format a printf-like string.

The helpfunction module involves four interfaces.

Interface introduction:

1.function printf(format: string, ...args: Object[]): string;

The util.format() method returns a formatted string using the first argument as a printf-like format string which can contain zero or more format specifiers. Each specifier is replaced with the converted value from the corresponding argument. Supported specifiers are:
        Each specifier is replaced with a converted value from the corresponding parameter. Supported specifiers are:
        %s: String will be used to convert all values except BigInt, Object and -0. BigInt values will be represented with an n and Objects that have no user defined toString function are inspected using util.inspect() with options { depth: 0, colors: false, compact: 3 }.
        %d: Number will be used to convert all values except BigInt and Symbol.
        %i: parseInt(value, 10) is used for all values except BigInt and Symbol.
        %f: parseFloat(value) is used for all values expect Symbol.
        %j: JSON. Replaced with the string '[Circular]' if the argument contains circular references.
        %o: Object. A string representation of an object with generic JavaScript object formatting. Similar to util.inspect() with options { showHidden: true, showProxy: true }. This will show the full object including non-enumerable properties and proxies.
        %O: Object. A string representation of an object with generic JavaScript object formatting. Similar to util.inspect() without options. This will show the full object not including non-enumerable properties and proxies.
        %c: CSS. This specifier is ignored and will skip any CSS passed in.
        %%: single percent sign ('%'). This does not consume an argument.
        Returns: <string> The formatted string
        If a specifier does not have a corresponding argument, it is not replaced:
        util.format('%s:%s', 'foo');
        // Returns: 'foo:%s'

Values that are not part of the format string are formatted using util.inspect() if their type is not string.
        If there are more arguments passed to the util.format() method than the number of specifiers, the extra arguments are         concatenated to the returned string, separated by spaces:
        util.format('%s:%s', 'foo', 'bar', 'baz');
        // Returns: 'foo:bar baz'

If the first argument does not contain a valid format specifier, util.format() returns a string that is the concatenation of all         arguments separated by spaces:
        util.format(1, 2, 3);
        // Returns: '1 2 3'

If only one argument is passed to util.format(), it is returned as it is without any formatting:
        util.format('%% %s');
        // Returns: '%% %s'

2.function getErrorString(errno: number): string;

The geterrorstring () method uses a system error number as a parameter to return system error information.

3.function callbackWrapper(original: Function): (err: Object, value: Object) => void;

Takes an async function (or a function that returns a Promise) and returns a function following the error-first callback style, i.e. taking an (err, value) => ... callback as the last argument. In the callback, the first argument will be the rejection reason (or null if the Promise resolved), and the second argument will be the resolved value.

4.function promiseWrapper(original: (err: Object, value: Object) => void): Object;

Takes a function following the common error-first callback style, i.e. taking an (err, value) => ... callback as the last argument, and returns a version that returns promises.

####2、 Method of use

Take printf and geterrorstring as examples:

1.printf()

{
        var format = "%%%o%%%i%s";

var value =  function aa(){};

var value1 = 1.5;

var value2 = "qwer";

var result = util.printf(format,value,value1,value2);
}

2.geterrorstring()

{
        var errnum = 13;

var result = util.geterrorstring(errnum);
}

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