add types for compare-func (#30630)

types/compare-func/compare-func-tests.ts

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+import compareFunc = require("compare-func");
+
+// This is taken from https://github.com/stevemao/compare-func/blob/master/README.md#usage and extended
+
+// sort by an object property
+[{ x: "b" }, { x: "a" }, { x: "c" }].sort(compareFunc("x"));
+// => [{x: "a"}, {x: "b"}, {x: "c"}]
+
+// sort by a nested object property
+[{ x: { y: "b" } }, { x: { y: "a" } }].sort(compareFunc("x.y"));
+// => [{x: {y: "a"}}, {x: {y: "b"}}]
+
+// sort by the `x` property, then `y`
+[{ x: "c", y: "c" }, { x: "b", y: "a" }, { x: "b", y: "b" }].sort(compareFunc(["x", "y"]));
+// => [{x: "b", y: "a"}, {x: "b", y: "b"}, {x: "c", y: "c"}]
+
+// sort by the returned value
+[{ x: "b" }, { x: "a" }, { x: "c" }].sort(compareFunc((el) => el.x));
+// => [{x: "a"}, {x: "b"}, {x: "c"}]
+
+// sort by an array of functions
+[{ x: "c", y: "c" }, { x: "b", y: "a" }, { x: "b", y: "b" }].sort(compareFunc([
+    (el) => el.x,
+    (el) => el.y,
+]));
+// => [{x: "a"}, {x: "b"}, {x: "c"}]
+
+// sort by itself
+[1, 3, 2].sort(compareFunc());
+// => [1, 2, 3]

types/compare-func/index.d.ts

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+// Type definitions for compare-func 1.3
+// Project: https://github.com/stevemao/compare-func
+// Definitions by: Dogan Fennibay <https://github.com/fennibay>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.4
+
+type extractFunc<T> = (e: T) => number | string;
+
+declare function compare_func<T>(prop?: ReadonlyArray<string | extractFunc<T>> | string | extractFunc<T>):
+    (e1: T, e2: T) => number;
+
+export = compare_func;

types/compare-func/tsconfig.json

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+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": true,
+        "strictFunctionTypes": true,
+        "baseUrl": "../",
+        "typeRoots": [
+            "../"
+        ],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "compare-func-tests.ts"
+    ]
+}

types/compare-func/tslint.json

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+{ "extends": "dtslint/dt.json" }