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awesome-typescript (opens new window)
# 第一题
「重学TS 2.0 」TS 练习题第一题 · Issue #19 · semlinker/awesome-typescript (github.com) (opens new window)
type User = {
id: number;
kind: string;
};
function makeCustomer<T extends User>(u: T): T {
// Error（TS 编译器版本：v4.4.2）
// Type '{ id: number; kind: string; }' is not assignable to type 'T'.
// '{ id: number; kind: string; }' is assignable to the constraint of type 'T',
// but 'T' could be instantiated with a different subtype of constraint 'User'.
return {
id: u.id,
kind: 'customer'
}
}
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思路：T 只是约束 User 类型，而不局限于User 类型，所以返回为T类型不仅仅只有 id 和 kind，需要一个接收其他类型的变量
type User = {
id: number;
kind: string;
};
function makeCustomer<T extends User>(u: T): T {
return {
...u,
id: u.id,
kind: 'customer'
}
}
makeCustomer({ id: 1, kind: '张三', name: '李四' })
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# 第二题
「重学TS 2.0 」TS 练习题第二题 · Issue #20 · semlinker/awesome-typescript (github.com) (opens new window)
function f(a: string | number, b: string | number) {
if (typeof a === 'string') {
return a + ':' + b; // no error but b can be number!
} else {
return a + b; // error as b can be number | string
}
}
f(2, 3); // Ok
f(1, 'a'); // Error
f('a', 2); // Error
f('a', 'b') // Ok
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思路
function f(a: string | number, b: string | number) {
if (typeof a === 'string' || typeof b === 'string') {
return a + ':' + b; // no error but b can be number!
} else {
return a + b; // error as b can be number | string
}
}
f(2, 3); // Ok
f(1, 'a'); // Error
f('a', 2); // Error
f('a', 'b') // Ok
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# 第三题
「重学TS 2.0 」TS 练习题第三题 · Issue #21 · semlinker/awesome-typescript (github.com) (opens new window)
1
