Declarations

Author: pirple-author

ES6/Declarations/const.js

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+/*
+ * Name: const
+ * Spec: https://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations
+ *
+ * WARNING / ATTENTION
+ * 1. Many of the examples in this file will throw an error. Don't try to run this file all at once, run them one by one.
+ * 2. A few of the examples (dealing with "this" and "window") will only work properly in a browser, not server-side
+ *
+ */
+
+// Declare variables but don't assign them a value;
+var var1;
+console.log("The declared but unassigned var1: ",var1, "has a type of: ",typeof(var1));
+const const1; // This should throw an error
+
+
+// Declare at higher scope and use at lower scope
+const const2 = 1;
+console.log("This is const2 before the if-statement ",const2);
+if('a' === 'a'){
+  console.log("This is const2 within the if-statement ",const2);
+}
+console.log("This is const2 after the if-statement ",const2);
+
+
+// Declare at higher scope and modify at lower scope, but use again at original scope unchanged
+const const3 = 1;
+console.log("This is const3 before the if-statement ",const3);
+if('a' === 'a'){
+  const const3 = 2;
+  console.log("This is const3 within the if-statement ",const3);
+}
+console.log("This is const3 after the if-statement ",const3);
+
+
+// Try to modify at the same level it was declared, omitting keyword
+const const4 = 1;
+const4 = 2;
+
+
+// Try to modify at the same level it was declared, with keyword
+const const5 = 1;
+const const5 = 2;
+
+
+// Declare at inner scope and try to use again at outer scope
+console.log("This is const6 before the if-statement ",typeof(const6));
+if('a' === 'a'){
+  const const6 = 2;
+  console.log("This is const6 within the if-statement ",const6);
+}
+console.log("This is const6 after the if-statement ",typeof(const6));
+
+
+// Declare at inner scope and declare again at outer scope
+if('a' === 'a'){
+  const const7 = 2;
+  console.log("This is const7 within the if-statement ",const7);
+}
+const const7 = 3;
+console.log("This is const7 after the if-statement ",const7);
+
+
+// Try to access a const that hasn't been declared yet but is declared below
+console.log("This is the type of const8 before we declare it",typeof(const8));
+const const8 = 1;
+
+// Declare a const object then try to change it to a different object
+const const9 = {
+  'foo' : 'bar'
+};
+const9 = {
+  'fizz' : 'buzz'
+};
+
+// Declare a const object then try to add a property
+const const10 = {
+  'foo' : 'bar'
+};
+const10.fizz = 'buzz';
+console.log("This is const10 after adding the new property ",const10);
+
+// Declare a const object then try to delete a property
+const const11 = {
+  'foo' : 'bar'
+};
+delete const11.foo;
+console.log("This is const11 after deleting the foo property ",const11);
+
+// Declare a const array then try to change it to a different array
+const const12 = ['foo','bar'];
+const12 = ['fizz','buzz'];
+
+// Declare a const array then try to add a value
+const const13 = ['foo','bar'];
+const13.push("fizz");
+console.log("This is const13 after adding the new value ",const13);
+
+// Declare a const array then try to delete a value
+const const14 = ['foo','bar'];
+const14.pop();
+console.log("This is const14 after deleting a foo value ",const14);

ES6/Declarations/let.js

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+/*
+ * Name: let
+ * Spec: https://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations
+ *
+ */
+
+
+// Declare variables but don't assign them a value;
+let let1;
+var var1;
+console.log("The declared but unassigned var1: ",var1, "has a type of: ",typeof(var1));
+console.log("The declared but unassigned let1: ",let1, "has a type of: ",typeof(let1));
+
+
+// Declare at higher scope and use at lower scope
+let let2 = 1;
+console.log("This is let2 before the if-statement ",let2);
+if('a' === 'a'){
+  console.log("This is let2 within the if-statement ",let2);
+}
+console.log("This is let2 after the if-statement ",let2);
+
+
+// Declare at higher scope and modify at lower scope, but use again at original scope unchanged
+let let3 = 1;
+console.log("This is let3 before the if-statement ",let3);
+if('a' === 'a'){
+  let let3 = 2;
+  console.log("This is let3 within the if-statement ",let3);
+}
+console.log("This is let3 after the if-statement ",let3);
+
+
+// Declare at inner scope and try to use again at outer scope
+console.log("This is let4 before the if-statement ",typeof(let4));
+if('a' === 'a'){
+  let let4 = 2;
+  console.log("This is let4 within the if-statement ",let4);
+}
+console.log("This is let4 after the if-statement ",typeof(let4));
+
+
+/*
+ * ATTENTION / WARNING
+ * The following 2 examples will only work properly within a browser window (not server-side)
+ *
+ */
+
+
+// Attempt to use 'this' at global scope
+let let5 = 1;
+var var2 = 1;
+console.log("This is the value of this.let5", typeof(this.let5));
+console.log("This is the value of this.var2",this.var2);
+
+// Attempt to use variables on the window opbject
+let let6 = 1;
+var var3 = 1;
+console.log("This is the value of window.let6", typeof(window.let6));
+console.log("This is the value of window.var3", window.var3);
+
+
+/*
+ * ATTENTION / WARNING
+ * Some of the following examples should throw an error
+ *
+ */
+
+// Try to re-declare the same variables (from the top of this page), with values
+var var1 = 0;
+console.log("This is the var1 with a value assigned to it ",var1);
+
+// Expect an error at this point. We can't "catch" this error because the try/catch statement introduces a new block level
+let let1 = 0;
+
+// Try to modify a let at the same level it was declared, with keyword
+let let7 = 1;
+let let7 = 2;
+
+// Try to modify a let at the same level it was declared, omitting keyword
+let let8 = 1;
+let8 = 2;
+console.log("This is the value of let8 now",let8);
+
+// Try to access a let that hasn't been declared yet but is declared below
+console.log("This is the type of let9 before we declare it",typeof(let9));
+let let9 = 1;