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java-script:strict-mode [2023/08/09 09:33] – odeftajava-script:strict-mode [2025/01/02 18:22] (current) – external edit 127.0.0.1
Line 41: Line 41:
  
 ===== Examples ===== ===== Examples =====
 +==== This will not fallback to window in strict mode ====
 +
 +<code javascript>
 +"use strict";
 +
 +function sayHello() {
 +  console.log(this.name, this.age);
 +}
 +
 +// ... rest of the code ...
 +
 +sayHello(); // TypeError: Cannot read properties of undefined (reading 'name')
 +</code>
 +In strict mode, **this** inside the **sayHello** function will be **undefined** when called without an object, leading to a TypeError when attempting to access properties on it.
 +
 +==== Cannot use global variables defined without var ====
  
 <code javascript> <code javascript>
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 x = 3.14; // This will throw an error because x is not declared. x = 3.14; // This will throw an error because x is not declared.
 </code> </code>
 +
 +==== Denial of usage of special variables / properties ====
  
 Assigning to Read-Only Global Variables and Properties: Assigning a value to a read-only property, a getter-only property, a non-writable global variable, or a non-writable property of an object will throw an error. Assigning to Read-Only Global Variables and Properties: Assigning a value to a read-only property, a getter-only property, a non-writable global variable, or a non-writable property of an object will throw an error.
Line 53: Line 71:
 undefined = "test"; // This will throw an error undefined = "test"; // This will throw an error
 </code> </code>
 +
 +==== Prevent the removal of variables / functions ====
  
 Deleting Variables, Functions, or Function Parameters: Attempting to delete variables, functions, or function parameters will throw an error. Deleting Variables, Functions, or Function Parameters: Attempting to delete variables, functions, or function parameters will throw an error.
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 delete x; // This will throw an error delete x; // This will throw an error
 </code> </code>
 +
 +==== Avoid duplicate parameter names ====
  
 Duplicate Parameter Names: Duplicate parameter names in function declarations will throw an error. Duplicate Parameter Names: Duplicate parameter names in function declarations will throw an error.
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 function x(p1, p1) {} // This will throw an error function x(p1, p1) {} // This will throw an error
 </code> </code>
 +
 +==== Deprecated octal syntax ====
  
 Octal Syntax: Octal syntax in ECMAScript 5 is deprecated, and strict mode will not allow it. Octal Syntax: Octal syntax in ECMAScript 5 is deprecated, and strict mode will not allow it.
java-script/strict-mode.1691573632.txt.gz · Last modified: (external edit)