[英]How to overload function by argument object shape in TypeScript?
Suppose I want to check the string's length, in 2 ways (fixed or range):假设我想以2 种方式(固定或范围)检查字符串的长度:
/* Fixed check */
check('abc', {length: 1}); // false
check('abc', {length: 3}); // true
/* Range check */
check('xyz', {minLength: 5, maxLength: 10}); // false
check('xyz', {minLength: 1, maxLength: 10}); // true
check('xyz', {minLength: 3, maxLength: 3}); // true
I first declared the 2 interfaces as follows:我首先声明了 2 个接口,如下所示:
interface StringFixed {
length: number;
}
interface StringRange {
minLength: number;
maxLength: number;
}
Then I try to write the function:然后我尝试写function:
function check(value: string, schema: StringFixed): boolean;
function check(value: string, schema: StringRange): boolean;
function check(value: string, schema: StringFixed | StringRange): boolean {
if (typeof schema.length !== 'undefined') { // ERROR
// Fixed check
} else {
// Range check
}
}
But now the TypeScript reports the ERROR in the first line of the function:但是现在 TypeScript 在 function 的第一行报告错误:
TS2339: Property 'length' does not exist on type 'StringFix | StringRange'
My question is how to do this in TypeScript?我的问题是如何在 TypeScript 中做到这一点?
You're so close.你是如此接近。 :-) You're asking for the type of the value of a property that you expect to be there (
typeof schema.length
). :-) 您正在询问您希望存在的属性值的类型(
typeof schema.length
)。 To implement a type guard , you want to ask if the property is there:要实现类型保护,您需要询问该属性是否存在:
if ("length" in schema) {
// Fixed check
} else {
// Range check
}
Working copy on the TypeScript playground . TypeScript 操场上的工作副本。
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