diff --git a/tests/baselines/reference/definiteAssignmentAssertions.errors.txt b/tests/baselines/reference/definiteAssignmentAssertions.errors.txt
new file mode 100644
index 00000000000..d65d9b510ae
--- /dev/null
+++ b/tests/baselines/reference/definiteAssignmentAssertions.errors.txt
@@ -0,0 +1,113 @@
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(5,5): error TS2564: Property 'b' has no initializer and is not definitely assigned in the constructor.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(20,6): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(21,6): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(22,13): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(28,6): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(34,15): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(68,10): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(69,10): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(70,10): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(75,15): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts(76,15): error TS1255: A definite assignment assertion '!' is not permitted in this context.
+
+
+==== tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts (11 errors) ====
+    // Suppress strict property initialization check
+    
+    class C1 {
+        a!: number;
+        b: string;  // Error
+        ~
+!!! error TS2564: Property 'b' has no initializer and is not definitely assigned in the constructor.
+    }
+    
+    // Suppress definite assignment check in constructor
+    
+    class C2 {
+        a!: number;
+        constructor() {
+            let x = this.a;
+        }
+    }
+    
+    // Definite assignment assertion requires type annotation, no initializer, no static modifier
+    
+    class C3 {
+        a! = 1;
+         ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+        b!: number = 1;
+         ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+        static c!: number;
+                ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    }
+    
+    // Definite assignment assertion not permitted in ambient context
+    
+    declare class C4 {
+        a!: number;
+         ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    }
+    
+    // Definite assignment assertion not permitted on abstract property
+    
+    abstract class C5 {
+        abstract a!: number;
+                  ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    }
+    
+    // Suppress definite assignment check for variable
+    
+    function f1() {
+        let x!: number;
+        let y = x;
+        var a!: number;
+        var b = a;
+    }
+    
+    function f2() {
+        let x!: string | number;
+        if (typeof x === "string") {
+            let s: string = x;
+        }
+        else {
+            let n: number = x;
+        }
+    }
+    
+    function f3() {
+        let x!: number;
+        const g = () => {
+            x = 1;
+        }
+        g();
+        let y = x;
+    }
+    
+    // Definite assignment assertion requires type annotation and no initializer
+    
+    function f4() {
+        let a!;
+             ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+        let b! = 1;
+             ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+        let c!: number = 1;
+             ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    }
+    
+    // Definite assignment assertion not permitted in ambient context
+    
+    declare let v1!: number;
+                  ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    declare var v2!: number;
+                  ~
+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/definiteAssignmentAssertions.js b/tests/baselines/reference/definiteAssignmentAssertions.js
new file mode 100644
index 00000000000..70bab1b9c23
--- /dev/null
+++ b/tests/baselines/reference/definiteAssignmentAssertions.js
@@ -0,0 +1,166 @@
+//// [definiteAssignmentAssertions.ts]
+// Suppress strict property initialization check
+
+class C1 {
+    a!: number;
+    b: string;  // Error
+}
+
+// Suppress definite assignment check in constructor
+
+class C2 {
+    a!: number;
+    constructor() {
+        let x = this.a;
+    }
+}
+
+// Definite assignment assertion requires type annotation, no initializer, no static modifier
+
+class C3 {
+    a! = 1;
+    b!: number = 1;
+    static c!: number;
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare class C4 {
+    a!: number;
+}
+
+// Definite assignment assertion not permitted on abstract property
+
+abstract class C5 {
+    abstract a!: number;
+}
+
+// Suppress definite assignment check for variable
+
+function f1() {
+    let x!: number;
+    let y = x;
+    var a!: number;
+    var b = a;
+}
+
+function f2() {
+    let x!: string | number;
+    if (typeof x === "string") {
+        let s: string = x;
+    }
+    else {
+        let n: number = x;
+    }
+}
+
+function f3() {
+    let x!: number;
+    const g = () => {
+        x = 1;
+    }
+    g();
+    let y = x;
+}
+
+// Definite assignment assertion requires type annotation and no initializer
+
+function f4() {
+    let a!;
+    let b! = 1;
+    let c!: number = 1;
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare let v1!: number;
+declare var v2!: number;
+
+
+//// [definiteAssignmentAssertions.js]
+"use strict";
+// Suppress strict property initialization check
+var C1 = /** @class */ (function () {
+    function C1() {
+    }
+    return C1;
+}());
+// Suppress definite assignment check in constructor
+var C2 = /** @class */ (function () {
+    function C2() {
+        var x = this.a;
+    }
+    return C2;
+}());
+// Definite assignment assertion requires type annotation, no initializer, no static modifier
+var C3 = /** @class */ (function () {
+    function C3() {
+        this.a = 1;
+        this.b = 1;
+    }
+    return C3;
+}());
+// Definite assignment assertion not permitted on abstract property
+var C5 = /** @class */ (function () {
+    function C5() {
+    }
+    return C5;
+}());
+// Suppress definite assignment check for variable
+function f1() {
+    var x;
+    var y = x;
+    var a;
+    var b = a;
+}
+function f2() {
+    var x;
+    if (typeof x === "string") {
+        var s = x;
+    }
+    else {
+        var n = x;
+    }
+}
+function f3() {
+    var x;
+    var g = function () {
+        x = 1;
+    };
+    g();
+    var y = x;
+}
+// Definite assignment assertion requires type annotation and no initializer
+function f4() {
+    var a;
+    var b = 1;
+    var c = 1;
+}
+
+
+//// [definiteAssignmentAssertions.d.ts]
+declare class C1 {
+    a: number;
+    b: string;
+}
+declare class C2 {
+    a: number;
+    constructor();
+}
+declare class C3 {
+    a: number;
+    b: number;
+    static c: number;
+}
+declare class C4 {
+    a: number;
+}
+declare abstract class C5 {
+    abstract a: number;
+}
+declare function f1(): void;
+declare function f2(): void;
+declare function f3(): void;
+declare function f4(): void;
+declare let v1: number;
+declare var v2: number;
diff --git a/tests/baselines/reference/definiteAssignmentAssertions.symbols b/tests/baselines/reference/definiteAssignmentAssertions.symbols
new file mode 100644
index 00000000000..a291172c83b
--- /dev/null
+++ b/tests/baselines/reference/definiteAssignmentAssertions.symbols
@@ -0,0 +1,146 @@
+=== tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts ===
+// Suppress strict property initialization check
+
+class C1 {
+>C1 : Symbol(C1, Decl(definiteAssignmentAssertions.ts, 0, 0))
+
+    a!: number;
+>a : Symbol(C1.a, Decl(definiteAssignmentAssertions.ts, 2, 10))
+
+    b: string;  // Error
+>b : Symbol(C1.b, Decl(definiteAssignmentAssertions.ts, 3, 15))
+}
+
+// Suppress definite assignment check in constructor
+
+class C2 {
+>C2 : Symbol(C2, Decl(definiteAssignmentAssertions.ts, 5, 1))
+
+    a!: number;
+>a : Symbol(C2.a, Decl(definiteAssignmentAssertions.ts, 9, 10))
+
+    constructor() {
+        let x = this.a;
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 12, 11))
+>this.a : Symbol(C2.a, Decl(definiteAssignmentAssertions.ts, 9, 10))
+>this : Symbol(C2, Decl(definiteAssignmentAssertions.ts, 5, 1))
+>a : Symbol(C2.a, Decl(definiteAssignmentAssertions.ts, 9, 10))
+    }
+}
+
+// Definite assignment assertion requires type annotation, no initializer, no static modifier
+
+class C3 {
+>C3 : Symbol(C3, Decl(definiteAssignmentAssertions.ts, 14, 1))
+
+    a! = 1;
+>a : Symbol(C3.a, Decl(definiteAssignmentAssertions.ts, 18, 10))
+
+    b!: number = 1;
+>b : Symbol(C3.b, Decl(definiteAssignmentAssertions.ts, 19, 11))
+
+    static c!: number;
+>c : Symbol(C3.c, Decl(definiteAssignmentAssertions.ts, 20, 19))
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare class C4 {
+>C4 : Symbol(C4, Decl(definiteAssignmentAssertions.ts, 22, 1))
+
+    a!: number;
+>a : Symbol(C4.a, Decl(definiteAssignmentAssertions.ts, 26, 18))
+}
+
+// Definite assignment assertion not permitted on abstract property
+
+abstract class C5 {
+>C5 : Symbol(C5, Decl(definiteAssignmentAssertions.ts, 28, 1))
+
+    abstract a!: number;
+>a : Symbol(C5.a, Decl(definiteAssignmentAssertions.ts, 32, 19))
+}
+
+// Suppress definite assignment check for variable
+
+function f1() {
+>f1 : Symbol(f1, Decl(definiteAssignmentAssertions.ts, 34, 1))
+
+    let x!: number;
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 39, 7))
+
+    let y = x;
+>y : Symbol(y, Decl(definiteAssignmentAssertions.ts, 40, 7))
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 39, 7))
+
+    var a!: number;
+>a : Symbol(a, Decl(definiteAssignmentAssertions.ts, 41, 7))
+
+    var b = a;
+>b : Symbol(b, Decl(definiteAssignmentAssertions.ts, 42, 7))
+>a : Symbol(a, Decl(definiteAssignmentAssertions.ts, 41, 7))
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(definiteAssignmentAssertions.ts, 43, 1))
+
+    let x!: string | number;
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 46, 7))
+
+    if (typeof x === "string") {
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 46, 7))
+
+        let s: string = x;
+>s : Symbol(s, Decl(definiteAssignmentAssertions.ts, 48, 11))
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 46, 7))
+    }
+    else {
+        let n: number = x;
+>n : Symbol(n, Decl(definiteAssignmentAssertions.ts, 51, 11))
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 46, 7))
+    }
+}
+
+function f3() {
+>f3 : Symbol(f3, Decl(definiteAssignmentAssertions.ts, 53, 1))
+
+    let x!: number;
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 56, 7))
+
+    const g = () => {
+>g : Symbol(g, Decl(definiteAssignmentAssertions.ts, 57, 9))
+
+        x = 1;
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 56, 7))
+    }
+    g();
+>g : Symbol(g, Decl(definiteAssignmentAssertions.ts, 57, 9))
+
+    let y = x;
+>y : Symbol(y, Decl(definiteAssignmentAssertions.ts, 61, 7))
+>x : Symbol(x, Decl(definiteAssignmentAssertions.ts, 56, 7))
+}
+
+// Definite assignment assertion requires type annotation and no initializer
+
+function f4() {
+>f4 : Symbol(f4, Decl(definiteAssignmentAssertions.ts, 62, 1))
+
+    let a!;
+>a : Symbol(a, Decl(definiteAssignmentAssertions.ts, 67, 7))
+
+    let b! = 1;
+>b : Symbol(b, Decl(definiteAssignmentAssertions.ts, 68, 7))
+
+    let c!: number = 1;
+>c : Symbol(c, Decl(definiteAssignmentAssertions.ts, 69, 7))
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare let v1!: number;
+>v1 : Symbol(v1, Decl(definiteAssignmentAssertions.ts, 74, 11))
+
+declare var v2!: number;
+>v2 : Symbol(v2, Decl(definiteAssignmentAssertions.ts, 75, 11))
+
diff --git a/tests/baselines/reference/definiteAssignmentAssertions.types b/tests/baselines/reference/definiteAssignmentAssertions.types
new file mode 100644
index 00000000000..92646bab86e
--- /dev/null
+++ b/tests/baselines/reference/definiteAssignmentAssertions.types
@@ -0,0 +1,157 @@
+=== tests/cases/conformance/controlFlow/definiteAssignmentAssertions.ts ===
+// Suppress strict property initialization check
+
+class C1 {
+>C1 : C1
+
+    a!: number;
+>a : number
+
+    b: string;  // Error
+>b : string
+}
+
+// Suppress definite assignment check in constructor
+
+class C2 {
+>C2 : C2
+
+    a!: number;
+>a : number
+
+    constructor() {
+        let x = this.a;
+>x : number
+>this.a : number
+>this : this
+>a : number
+    }
+}
+
+// Definite assignment assertion requires type annotation, no initializer, no static modifier
+
+class C3 {
+>C3 : C3
+
+    a! = 1;
+>a : number
+>1 : 1
+
+    b!: number = 1;
+>b : number
+>1 : 1
+
+    static c!: number;
+>c : number
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare class C4 {
+>C4 : C4
+
+    a!: number;
+>a : number
+}
+
+// Definite assignment assertion not permitted on abstract property
+
+abstract class C5 {
+>C5 : C5
+
+    abstract a!: number;
+>a : number
+}
+
+// Suppress definite assignment check for variable
+
+function f1() {
+>f1 : () => void
+
+    let x!: number;
+>x : number
+
+    let y = x;
+>y : number
+>x : number
+
+    var a!: number;
+>a : number
+
+    var b = a;
+>b : number
+>a : number
+}
+
+function f2() {
+>f2 : () => void
+
+    let x!: string | number;
+>x : string | number
+
+    if (typeof x === "string") {
+>typeof x === "string" : boolean
+>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : string | number
+>"string" : "string"
+
+        let s: string = x;
+>s : string
+>x : string
+    }
+    else {
+        let n: number = x;
+>n : number
+>x : number
+    }
+}
+
+function f3() {
+>f3 : () => void
+
+    let x!: number;
+>x : number
+
+    const g = () => {
+>g : () => void
+>() => {        x = 1;    } : () => void
+
+        x = 1;
+>x = 1 : 1
+>x : number
+>1 : 1
+    }
+    g();
+>g() : void
+>g : () => void
+
+    let y = x;
+>y : number
+>x : number
+}
+
+// Definite assignment assertion requires type annotation and no initializer
+
+function f4() {
+>f4 : () => void
+
+    let a!;
+>a : any
+
+    let b! = 1;
+>b : number
+>1 : 1
+
+    let c!: number = 1;
+>c : number
+>1 : 1
+}
+
+// Definite assignment assertion not permitted in ambient context
+
+declare let v1!: number;
+>v1 : number
+
+declare var v2!: number;
+>v2 : number
+