51 lines
1.1 KiB
JavaScript
51 lines
1.1 KiB
JavaScript
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// @flow
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function foo1(o: { x: number }) {
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if (o.p1) { // OK, this is an idiomatic way of testing property existence
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o.x;
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}
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}
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function foo2(o: { x: number }) {
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if (o.p2) { // OK
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o.p2.x; // error, since o.p2's type is unknown (e.g., could be `number`)
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}
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}
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function foo3(o: { x: number }) {
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o.p3.x; // usual error outside conditional
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}
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function foo4(o: $Exact<{ x: number }>) {
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if (o.p4) { // OK
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o.p4.x; // currently OK, should be unreachable
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} else {
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o.p4.x; // error
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}
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}
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function foo5() {
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const o = { };
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_foo5();
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if (o.p) { o.p(); }
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function _foo5() {
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o.p = function() { }
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}
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}
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function foo6(o: mixed) {
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if (o.bar) {} // error, any lookup on mixed is unsafe
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}
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function foo7(o: mixed) {
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if (typeof o.bar === 'string') {} // error
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if (o && typeof o.bar === 'string') {} // ok
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if (o != null && typeof o.bar === 'string') {} // ok
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if (o !== null && o !== undefined && typeof o.bar === 'string') {} // ok
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}
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function foo8(o: { p: mixed }) {
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if (o.p && o.p.q) {} // this is ok because o.p is truthy, so o.p.q is safe
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if (o.p && o.p.q && o.p.q.r) {}
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}
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