TypeScript study notes (b)

Block-level scope variables:

　　1, not being read or written statement before

the console.log (NUM); 
the let NUM: Number = 0;     // given

　　2, can still have a variable declaration before the block-level scope to capture it through the function, but can not go calling this function in the variable declaration

function Test () {
     return num; 
} 

Test ();     // can not call is declared before num Test 

the let num: Number = 0;

　　3, block-level scope variables of the same name to be in different blocks declared in

Note: var variable declaration has function scope, there is a statement in advance , so no matter the statement several times, will get the same variable

 

interface:

　　1, the interface keyword interface to define

　　2, TypeScript, the role of these interfaces is named type and your code or third-party code defined contract and make code look better understanding

　　3, type checker not to check the object implements this interface attributes in order , as long as the corresponding attribute is present and the type of a corresponding identical to

　　4, optional attributes: It is not necessary to attribute declaration form attrName ?: type

{obj interface 
    width : Number;?     // an optional attribute 
    HEIGH: Number;     // a common attribute
     Readonly Shape: String;     // read-only property
 }

Note: The optional attribute can be possible to attribute pre-defined , can capture cited nonexistent property at the time of the error

　　5, read-only attribute: attribute name used before readonly designated read-only attribute, only the value is modified when the object is newly created, the array having unmodifiable typescript ReadonlyArray <T> Type

let roArr: Readonly<number> = [1, 2, 3];
let arr_one: Array<number> = roArr;    // 报错
let arr_two: Array<number> = roArr as Array<number>;    // 编译通过

Note: The ReadonlyArray not assigned to a regular array, but you can override the type of assertion

　　6, when for the attribute when should Readonly , for the variable time should const

 

Function type:

　　1, the interface can be described in a wide variety of configurations JavaScript objects have, in addition to describe a common object with attributes, but it can also be a function of the type described

　　2, need to interface defines a call signature , just like a list of parameters and return value type of functions "== Each parameter requires the name and type

interface SearchFunc {
    // 调用签名
    (source: string, subString: string): boolean;
}
let mySearch: SearchFunc;
mySearch = function (source: string, subString: string) {
    return source.search(subString) > -1;
}
let str: string = "Hello World";
alert(mySearch(str, "world"));    // 弹出 false

Note: The parameter name of the function does not need to match the name defined in the interface, parameters one by one to be checked ,

       Parameters corresponding to a position required type is compatible , if not specified type, typescript will deduce the parameters of Type

 

Indexable type:

　　1, similar to the type and function, but with an index signature , which describes the object type of the index , as well as the respective type returned index

　　2, TypeScript support string and numeric index neither index signature, which can use two types of indexes, the numerical index value must be a return string index return type subtype

interface StringArray {
    // 索引签名
    [index: number]: string;
}

let myArray: StringArray;

myArray = ["Lemon", "Yam"];

alert(myArray[0]);

NOTE: When simultaneously using two index signature, digital is converted into a string index Index

 

Class type:

　　1, use it to clear a class forced to comply with a contractual

　　2, has two types of class: static part type and of the Examples section type

　　3, when a class that implements the interface, only examples of its type checking portion

　　4, when a class inherits the interface type, it inherits the members of the class, but does not include its implementation , the interface will also inherit the class private and protected members

Note: private and protected members can only be achieved in this class or subclass