TypeScript Union Types
Union Types allow variables to be set to multiple types using the pipe (|) symbol, and values can be assigned according to the set types.
Note: Only the specified types can be assigned; assigning other types will cause an error.
The syntax for creating a union type is as follows:
Type1|Type2|Type3
Example
Declare a union type:
TypeScript
var val:string|number
val = 12
console.log("The number is"+ val)
val = "Example"
console.log("The string is" + val)
Compile the above code to get the following JavaScript code:
JavaScript
var val;
val = 12;
console.log("The number is" + val);
val = "Example";
console.log("The string is" + val);
The output result is:
数字为 12 字符串为 Example
Assigning other types will cause an error:
var val:string|number val = true
You can also use union types as function parameters:
TypeScript
function disp(name:string|string[]) {
if(typeof name == "string") {
console.log(name)
} else {
var i;
for(i = 0;i<name.length;i++) {
console.log(name[i])
}
}
}
disp("Example")
console.log("Output array....")
disp(["Example","Google","Taobao","Facebook"])
Compile the above code to get the following JavaScript code:
JavaScript
function disp(name) {
if (typeof name == "string") {
console.log(name);
}
else {
var i;
for (i = 0; i < name.length; i++) {
console.log(name[i]);
}
}
}
disp("Example");
console.log("Output array....");
disp(["Example", "Google", "Taobao", "Facebook"]);
The output result is:
Example 输出数组.... Example Google Taobao Facebook
Union Type Arrays
We can also declare arrays as union types:
TypeScript
var arr:number[]|string[];
var i:number;
arr = [1,2,4]
console.log("**Number array**")
for(i = 0;i<arr.length;i++) {
console.log(arr[i])
}
arr = ["Example","Google","Taobao"]
console.log("**String array**")
for(i = 0;i<arr.length;i++) {
console.log(arr[i])
}
Compile the above code to get the following JavaScript code:
JavaScript
var arr;
var i;
arr = [1, 2, 4];
console.log("**Number array**");
for (i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
arr = ["Example", "Google", "Taobao"];
console.log("**String array**");
for (i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
The output result is:
**数字数组** 1 2 4 **字符串数组** Example Google TaobaoOther Extensions