Most Imp Js

Author: nilajcoder

JavaScript Interview/Most Imp MCQ/demo.js

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+/*
+
+** Four Example of falsy values in JS
+
+1. undefined
+var a;
+console.log(typeof(a));// undefined
+console.log(Boolean(a)); // false
+
+
+ 2. null
+var a = null;
+console.log(typeof(a));// object
+console.log(Boolean(a));// false
+
+
+ 3. NaN
+var a = NaN;
+console.log(typeof(a));// number
+console.log(Boolean(a));// false
+
+
+ 4. 0
+var a = 0;
+console.log(typeof(a));// number
+console.log(Boolean(a));// false
+
+
+ 5. "" (empty string)
+var a = "";
+console.log(typeof(a));// string
+console.log(Boolean(a));// false
+
+
+** let b;
+console.log(b);// undefined
+
+
+** var a;
+console.log(a);// undefined
+
+
+** const a;
+console.log(a);// SyntaxError: Missing initializer in const declaration
+
+
+**
+
+console.log(a); // ReferenceError: Cannot access 'a' before initialization
+let a = 10;
+
+
+**
+console.log(a); // undefined
+var a; // undefined
+
+
+**
+console.log(a); // ReferenceError: Cannot access 'a' before initialization
+const a;
+
+
+**
+console.log(name);// undefined
+var name;
+
+1. {
+    let a = 1;
+    let b = 2;
+
+    console.log(a);// 1
+    console.log(b);// 2
+}
+
+console.log(a); // ReferenceError: a is not defined
+console.log(b); // ReferenceError: b is not defined
+
+
+
+2. {
+    const a = 1;
+    const b = 2;
+
+    console.log(a);// 1
+    console.log(b);// 2
+}
+
+console.log(a); // ReferenceError: a is not defined
+console.log(b);// ReferenceError: b is not defined
+
+
+
+3. {
+    var a = 1;
+    var b = 2;
+
+    console.log(a);// 1
+    console.log(b);// 2
+}
+
+console.log(a); // 1
+console.log(b); // 2
+
+
+
+4. console.log(a);// undefined
+var a = 1;
+console.log(a); // 1
+
+
+5. console.log(a); // referenceError: a is not defined
+let a = 1;
+console.log(a); 
+
+
+6. 
+console.log(a); // referenceError: a is not defined
+const  a = 1;
+console.log(a); 
+
+
+7. 
+console.log(name);// undefined
+var name = 'John Doe';
+*/
+
+
+