æŽæ°ïŒç§ã®ææ°ã®ææ¡ã«ã€ããŠã¯ãã³ã¡ã³ãhttps://github.com/Microsoft/TypeScript/issues/13778#issuecomment-406316164ãåç §ããŠ
strictNullChecks
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äŸïŒ
const xs: number[] = [1,2,3];
xs[100] // number, even with strictNullChecks
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const xs: number[] = [1,2,3];
xs[100] // number | undefined
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lib.d.ts
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{
// https://github.com/Microsoft/TypeScript/blob/1f92bacdc81e7ae6706ad8776121e1db986a8b27/lib/lib.d.ts#L1300
declare global {
interface Array<T> {
[n: number]: T | undefined;
}
}
const xs = [1,2,3]
const x = xs[100]
x // still number :-(
}
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ãšããã€ã³ããã¯ã¹ã®çœ²åã[n: number]: T | undefined;
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var a = [];
for (var i =0; i< a.length; i++) {
a[i]+=1; // a[i] is possibly undefined
}
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var a = [];
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if (a[i]) {
a[i]+=1; // a[i] is possibly undefined
}
}
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let a: number[] = []
a[0] = 0
a[5] =0
for (let i = 0; i < a.length; i++) {
console.log(a[i])
}
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ç§ã¯ãã®ã³ã¡ã³ãã§ããå°ãæšè«ã«å ¥ããŸããhttps://github.com/Microsoft/TypeScript/issues/11238#issuecomment-250562397
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for (let i = 0; i < arr.length; i++) {
// arr[i] is T, not T | undefined
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for (const k of Object.keys(obj)) {
// obj[k] is T, not T | undefined
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for (let i = 0; i < arr.length; i++) {
console.log(arr[i].name);
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for (let i = 0; i < arr.length; i++) {
// TypeScript makes me use ! with my arrays, sad.
console.log(arr[i]!.name);
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function doSomething(myObj: T, yourObj: T) {
for (const k of Object.keys(myObj)) {
console.log(yourObj[k].name);
}
}
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function doSomething(myObj: T, yourObj: T) {
for (const k of Object.keys(myObj)) {
console.log(yourObj[k]!.name); // Shut up TypeScript I know what I'm doing
}
}
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}
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}
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n['foo']
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Object.values(n)
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n['foo'] = undefined;
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delete n['foo'];
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delete o['foo'];
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class Foo {
foo: string | number = 123
bar() {
this.foo = 'bar'
}
broken() {
if (typeof this.foo === 'number') {
this.bar();
this.foo.toLowerCase(); // right, but type error
this.foo.toExponential(); // wrong, but typechecks
}
}
}
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//arr is of type [string, string, string]
}
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//arr is of type [string, string, string, string, ...string[]]
}
if (arr.length) {
//arr is of type [string, ...string[]]
}
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if (arr.length > 0) {
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}
}
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let someNumber = 55;
if (arr.length) {
let el1 = arr[0]; //string
let el2 = arr[1]; //string | undefined
let el3 = arr[someNumber]; //string | undefined
}
if(arr.length >= 3){
let [el1, el2, el3, el4] = arr;
//el1, el2, el3 are string
// el4 is string | undefined
}
if (arr.length == 2){
let [el1, el2, el3] = arr; //compiler error: "Tuple type '[string, string]' with length '2' cannot be assigned to tuple with length '3'.",
}
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}
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declare const array: (number | undefined)[];
const first = array[0]; // number | undefined, as desired :-)
type IndexValue = typeof array[0]; // number | undefined, as desired! :-)
array.map(x => {
x // number | undefined, not desired! :-(
})
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const first = array[0]; // number | undefined, as desired :-)
type IndexValue = typeof array[0]; // number | undefined, as desired :-)
array.map(x => {
x // number, as desired :-)
})
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for (let i = 0; i < array.length; i++) {
const x = array[i];
x; // number | undefined, not desired! :-(
}
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for (let i = 0; i < array.length; i++) {
const x = array[i]!;
x; // number, as desired :-)
}
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declare const array: { [index: number]!!: string };
declare const dictionary: { [index: string]!!: string }
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declare const dictionary: { [index: string]??: string }
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@ buu700 TypeScript 3.0ãžããããïŒ https ïŒ //blogs.msdn.microsoft.com/typescript/2018/07/30/announcing-typescript-3-0/#richer -tuple-types
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const array = [1, 2, 3];
for (var i =0; i< array.length; i++) {
array[i]+=1; // array[i] is possibly undefined
}
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const array = [1, 2, 3];
array.forEach((value, i) => array[i] = value + 1);
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return map[index];
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"a": 1,
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};
const test = obj["c"]; // const test: number
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src={savedAdsItem.advertImageList.advertImage[0].mainImageUrl || undefined}
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birthYear: profileData.birthYear !== null ? profileData.birthYear : allowedYears[0].value,
upsellingsList.upsellingProducts[0].upsellingProducts[0].selected = true
const latitude = parseFloat(coordinates.split(',')[0])
const advert = Object.values(actionToConfirm.selectedItems)[0]
await dispatch(deactivateMyAd(advert))
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}
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declare function someFunc(arr: number[], i: number): void;
let arr = [1, 2, 3, 4];
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someFunc(arr, arr[i]);
}
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let arr = [1, 2, 3, 4];
let alias = arr;
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someFunc(alias, arr[i]);
}
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arr[7] = 7
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}
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@tobico https://github.com/microsoft/TypeScript/issues/13778#issuecomment -536248028
@danielnixonããã¯è§£æ±ºçã§ã¯ãªããåé¿çã§ãã ããªããä»ã®éçºè ãåãç®çã®ããã«èšèªã®çµã¿èŸŒã¿ããŒã«ã誀ã£ãŠäœ¿çšããããšã劚ãããã®ã¯äœããããŸããïŒããªããããããããšåŒã¶ããšããã§ããã°ïŒã ã€ãŸããç§ã¯ãã®ãããªãã®ã«fp-tsã䜿çšããŠããŸããããã®åé¡ã¯ãŸã æå¹ã§ãããä¿®æ£ããå¿ èŠããããŸãã
@RyanCavanaughããã®è°è«ã次ã®ããã«ãã©ãããšãã§ããŸããïŒ
for (let i = 0; i < arr.length; i++) {
// TypeScript makes me use ! with my arrays, sad.
console.log(arr[i]!.name);
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const x = ['a', 'b', 'c']
console.log(x[3]) // type: string, reality: undefined
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const x = ['a', 'b', 'c'] as const
console.log(x[3]) // compile error: Tuple type 'readonly ["a", "b", "c"]' of length '3' has no element at index '3'.ts(2493)
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type ArrayValueType<A extends { [n: number]: unknown }> = (
A extends Array<infer T> ? T :
A extends ReadonlyArray<infer T> ? T :
A[number] // Fall back to old way of getting array element type
);
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declare const t : T;
obj["k"] = t; //ok
obj["k"] = undefined; //error, undefined not assignable to T
//T|undefined inferred,
//since we don't know if "k2" is an "ownProperty" of obj
const v = obj["k2"];
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}
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