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Merge pull request #10009 from Microsoft/null-undefined-allowed-as-index-expressions
`Null` and `undefined` are allowed as index expressions
2 parents 9cc8b2e + e2709d8 commit 01aaff7

8 files changed

+199
-2
lines changed

‎src/compiler/checker.ts

Lines changed: 3 additions & 2 deletions
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@@ -10842,10 +10842,11 @@ namespace ts {
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}
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// Check for compatible indexer types.
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if (isTypeAnyOrAllConstituentTypesHaveKind(indexType, TypeFlags.StringLike | TypeFlags.NumberLike | TypeFlags.ESSymbol)) {
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const allowedNullableFlags = strictNullChecks ? 0 : TypeFlags.Nullable;
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if (isTypeAnyOrAllConstituentTypesHaveKind(indexType, TypeFlags.StringLike | TypeFlags.NumberLike | TypeFlags.ESSymbol | allowedNullableFlags)) {
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// Try to use a number indexer.
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if (isTypeAnyOrAllConstituentTypesHaveKind(indexType, TypeFlags.NumberLike) || isForInVariableForNumericPropertyNames(node.argumentExpression)) {
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if (isTypeAnyOrAllConstituentTypesHaveKind(indexType, TypeFlags.NumberLike | allowedNullableFlags) || isForInVariableForNumericPropertyNames(node.argumentExpression)) {
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const numberIndexInfo = getIndexInfoOfType(objectType, IndexKind.Number);
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if (numberIndexInfo) {
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getNodeLinks(node).resolvedIndexInfo = numberIndexInfo;

‎tests/baselines/reference/indexWithUndefinedAndNull.js

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//// [indexWithUndefinedAndNull.ts]
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interface N {
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[n: number]: string;
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}
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interface S {
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[s: string]: number;
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}
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let n: N;
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let s: S;
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let str: string = n[undefined];
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str = n[null];
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let num: number = s[undefined];
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num = s[null];
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//// [indexWithUndefinedAndNull.js]
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var n;
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var s;
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var str = n[undefined];
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str = n[null];
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var num = s[undefined];
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num = s[null];

‎tests/baselines/reference/indexWithUndefinedAndNull.symbols

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=== tests/cases/compiler/indexWithUndefinedAndNull.ts ===
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interface N {
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>N : Symbol(N, Decl(indexWithUndefinedAndNull.ts, 0, 0))
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[n: number]: string;
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>n : Symbol(n, Decl(indexWithUndefinedAndNull.ts, 1, 5))
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}
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interface S {
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>S : Symbol(S, Decl(indexWithUndefinedAndNull.ts, 2, 1))
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[s: string]: number;
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>s : Symbol(s, Decl(indexWithUndefinedAndNull.ts, 4, 5))
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}
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let n: N;
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>n : Symbol(n, Decl(indexWithUndefinedAndNull.ts, 6, 3))
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>N : Symbol(N, Decl(indexWithUndefinedAndNull.ts, 0, 0))
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let s: S;
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>s : Symbol(s, Decl(indexWithUndefinedAndNull.ts, 7, 3))
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>S : Symbol(S, Decl(indexWithUndefinedAndNull.ts, 2, 1))
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let str: string = n[undefined];
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>str : Symbol(str, Decl(indexWithUndefinedAndNull.ts, 8, 3))
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>n : Symbol(n, Decl(indexWithUndefinedAndNull.ts, 6, 3))
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>undefined : Symbol(undefined)
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str = n[null];
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>str : Symbol(str, Decl(indexWithUndefinedAndNull.ts, 8, 3))
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>n : Symbol(n, Decl(indexWithUndefinedAndNull.ts, 6, 3))
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let num: number = s[undefined];
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>num : Symbol(num, Decl(indexWithUndefinedAndNull.ts, 10, 3))
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>s : Symbol(s, Decl(indexWithUndefinedAndNull.ts, 7, 3))
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>undefined : Symbol(undefined)
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num = s[null];
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>num : Symbol(num, Decl(indexWithUndefinedAndNull.ts, 10, 3))
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>s : Symbol(s, Decl(indexWithUndefinedAndNull.ts, 7, 3))
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‎tests/baselines/reference/indexWithUndefinedAndNull.types

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=== tests/cases/compiler/indexWithUndefinedAndNull.ts ===
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interface N {
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>N : N
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[n: number]: string;
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>n : number
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}
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interface S {
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>S : S
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[s: string]: number;
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>s : string
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}
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let n: N;
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>n : N
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>N : N
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let s: S;
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>s : S
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>S : S
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let str: string = n[undefined];
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>str : string
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>n[undefined] : string
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>n : N
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>undefined : undefined
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str = n[null];
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>str = n[null] : string
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>str : string
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>n[null] : string
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>n : N
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>null : null
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let num: number = s[undefined];
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>num : number
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>s[undefined] : number
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>s : S
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>undefined : undefined
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num = s[null];
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>num = s[null] : number
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>num : number
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>s[null] : number
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>s : S
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>null : null
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‎tests/baselines/reference/indexWithUndefinedAndNullStrictNullChecks.errors.txt

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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(9,19): error TS2454: Variable 'n' is used before being assigned.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(9,19): error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(10,7): error TS2454: Variable 'n' is used before being assigned.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(10,7): error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(11,19): error TS2454: Variable 's' is used before being assigned.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(11,19): error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(12,7): error TS2454: Variable 's' is used before being assigned.
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tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts(12,7): error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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==== tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts (8 errors) ====
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interface N {
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[n: number]: string;
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}
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interface S {
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[s: string]: number;
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}
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let n: N;
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let s: S;
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let str: string = n[undefined];
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~
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!!! error TS2454: Variable 'n' is used before being assigned.
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~~~~~~~~~~~~
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!!! error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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str = n[null];
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~
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!!! error TS2454: Variable 'n' is used before being assigned.
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~~~~~~~
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!!! error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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let num: number = s[undefined];
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~
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!!! error TS2454: Variable 's' is used before being assigned.
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~~~~~~~~~~~~
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!!! error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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num = s[null];
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~
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!!! error TS2454: Variable 's' is used before being assigned.
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~~~~~~~
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!!! error TS2342: An index expression argument must be of type 'string', 'number', 'symbol', or 'any'.
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‎tests/baselines/reference/indexWithUndefinedAndNullStrictNullChecks.js

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//// [indexWithUndefinedAndNullStrictNullChecks.ts]
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interface N {
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[n: number]: string;
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}
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interface S {
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[s: string]: number;
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}
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let n: N;
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let s: S;
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let str: string = n[undefined];
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str = n[null];
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let num: number = s[undefined];
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num = s[null];
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//// [indexWithUndefinedAndNullStrictNullChecks.js]
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var n;
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var s;
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var str = n[undefined];
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str = n[null];
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var num = s[undefined];
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num = s[null];

‎tests/cases/compiler/indexWithUndefinedAndNull.ts

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// @strictNullChecks: false
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interface N {
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[n: number]: string;
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}
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interface S {
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[s: string]: number;
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}
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let n: N;
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let s: S;
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let str: string = n[undefined];
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str = n[null];
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let num: number = s[undefined];
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num = s[null];

‎tests/cases/compiler/indexWithUndefinedAndNullStrictNullChecks.ts

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// @strictNullChecks: true
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interface N {
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[n: number]: string;
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}
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interface S {
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[s: string]: number;
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}
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let n: N;
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let s: S;
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let str: string = n[undefined];
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str = n[null];
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let num: number = s[undefined];
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num = s[null];

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