fix: #1609 resolve .length on array interpolation params

Widen the isArray branch of getValue() to short-circuit on a terminal
"length" key, and gate numeric-index lookups behind a /^\d+$/ regex so
malformed keys like "1x", "1.5", and "-1" are rejected (parseInt would
otherwise parse leading digits and silently accept them).

Adds unit tests pinning the contract (length works, prototype props
like constructor/toString/push remain inaccessible, length.foo is
terminal) plus a parser-level regression guard for the original
{{array.length}} interpolation case.

Fixes #1609

Author: CodeAndWeb

projects/ngx-translate/src/lib/util.ts

@@ -154,15 +154,22 @@ export function getValue(target: unknown, key: string): unknown {
             }
 
             if (isArray(target)) {
-                const index = parseInt(key, 10);
-                if (
-                    isDefined(target[index]) &&
-                    (isDict(target[index]) || isArray(target[index]) || isLastKey)
-                ) {
-                    target = target[index];
+                if (key === "length" && isLastKey) {
+                    target = target.length;
                     key = "";
                     continue;
                 }
+                if (/^\d+$/.test(key)) {
+                    const index = parseInt(key, 10);
+                    if (
+                        isDefined(target[index]) &&
+                        (isDict(target[index]) || isArray(target[index]) || isLastKey)
+                    ) {
+                        target = target[index];
+                        key = "";
+                        continue;
+                    }
+                }
             }
         }
 

projects/ngx-translate/src/tests/translate.parser.spec.ts

@@ -35,6 +35,20 @@ describe("Parser", () => {
             ).toEqual("This is a value3");
         });
 
+        it("should interpolate an array's length (regression #1609)", () => {
+            expect(
+                parser.interpolate("Found {{matches.length}} items", {
+                    matches: ["a", "b", "c"],
+                }),
+            ).toEqual("Found 3 items");
+
+            expect(
+                parser.interpolate("You have {{items.length}} messages", {
+                    items: [],
+                }),
+            ).toEqual("You have 0 messages");
+        });
+
         it("should support interpolation functions", () => {
             const uc: InterpolateFunction = (params) => {
                 return (getValue(params, "x") as string)?.toUpperCase() + " YOU!";

projects/ngx-translate/src/tests/utils.spec.ts

@@ -226,6 +226,24 @@ describe("Utils", () => {
             expect(getValue(["A", ["a", "b", "c"], "C"], "1.2")).toEqual("c");
 
             expect(getValue("test", "key")).not.toBeDefined();
+
+            // length property on arrays — regression guard for #1609
+            expect(getValue([1, 2, 3], "length")).toEqual(3);
+            expect(getValue([], "length")).toEqual(0);
+            expect(getValue({ matches: ["a", "b", "c"] }, "matches.length")).toEqual(3);
+
+            // malformed numeric keys are rejected (parseInt-leading-digits loophole)
+            expect(getValue([1, 2, 3], "1x")).not.toBeDefined();
+            expect(getValue([1, 2, 3], "1.5")).not.toBeDefined();
+            expect(getValue([1, 2, 3], "-1")).not.toBeDefined();
+
+            // tight contract: other array properties are NOT exposed via getValue
+            expect(getValue([1, 2, 3], "constructor")).not.toBeDefined();
+            expect(getValue([1, 2, 3], "toString")).not.toBeDefined();
+            expect(getValue([1, 2, 3], "push")).not.toBeDefined();
+
+            // length is terminal — chaining past it returns undefined
+            expect(getValue([1, 2, 3], "length.foo")).not.toBeDefined();
         });
     });