Created
December 18, 2019 04:58
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ts unknown test
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let value1: any; | |
value1 = true; // OK | |
value1 = 42; // OK | |
value1 = "Hello World"; // OK | |
value1 = []; // OK | |
value1 = {}; // OK | |
value1 = Math.random; // OK | |
value1 = null; // OK | |
value1 = undefined; // OK | |
value1 = new TypeError(); // OK | |
// Math.max(...value1); // コンパイルOK、実行時にnumberの配列でないとエラーになる | |
let value2: unknown; | |
value2 = true; // OK | |
value2 = 42; // OK | |
value2 = "Hello World"; // OK | |
value2 = []; // OK | |
value2 = {}; // OK | |
value2 = Math.random; // OK | |
value2 = null; // OK | |
value2 = undefined; // OK | |
value2 = new TypeError(); // OK | |
value2 = [1, 2, 3]; | |
Math.max(...value2); // Type 'unknown' is not an array type. ←unknownだとエラーになってくれるので型安全! | |
if (isNumberArray(value2)) { | |
console.log(Math.max(...value2)); // numberの配列のチェック後などに実行可能! | |
} | |
function isNumberArray(value: unknown): value is number[] { | |
return ( | |
Array.isArray(value) && | |
value.every(element => typeof element === "number") | |
); | |
} | |
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