How to solve 'javascript is not defined'

JavaScript (JS for short) is a widely used dynamic scripting language used in web development, application development, game development and other fields. As one of the most popular programming languages, JavaScript plays an irreplaceable role in modern web development due to its rich library and frameworks.

However, although JavaScript has become one of the mainstream languages ​​​​in the programming field, JavaScript programming still faces a problem that irritates many developers - "JavaScript is not defined".

When this happens, it is usually caused by the required variables not being defined in the code. When executing the code, the JavaScript compiler cannot find the definition of the variable and therefore throws the "JavaScript not defined" error.

In many cases, this error is often caused by developer negligence, such as forgetting to declare variables, using incorrectly spelled variable names, etc. For example, when operating with an undefined variable, such as:

var number = 5;
sum = number + value;

The above code will throw a "JavaScript is not defined" error because in the second line of code, the variable "value" does not is defined, so no operations can be performed.

Another situation is that the variable has been declared, but the definition of the variable cannot be found in the current scope. For example:

function addNumbers(a, b){
  var sum = a + b;
  return sum;
}

console.log(sum);

In this example, we define a function called "addNumbers" that returns the sum of two numbers. A variable named "sum" is used inside the function to store the sum. However, trying to access this variable from outside a function will throw a "JavaScript not defined" error.

The easiest way to solve this problem is to declare the variables defined inside the function as global variables. For example:

var sum;

function addNumbers(a, b){
  sum = a + b;
  return sum;
}

console.log(sum);

Doing this will allow the variable "sum" to be accessed outside the function, avoiding "JavaScript not defined" errors.

In addition to using variables undefined, another common mistake is to refer to objects and functions undefined. This usually happens when the object or function name is misspelled or when the function is outside the scope. For example:

var person = {
  name: "John",
  age: 30,
  hobbies: ["reading", "music", "swimming"],
  greet: function(){
    console.log("Hello, my name is " + this.name);
  }
};

peron.greet();

The above code contains an object "person" which contains a function named "greet". However, there is a typo in the code: "peron" instead of "person". This will result in a "JavaScript not defined" error and the function "greet" will not be accessible.

When debugging JavaScript code, it is very common to see the error "JavaScript is not defined". However, these errors are usually easy to fix by carefully reviewing your code and making sure that all variables and functions are properly declared and defined. Once such errors are fixed, normal operation of the JavaScript code can be quickly restored.

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