When the page is reloaded, JavaScript code remains unprocessed

Question

When the page is reloaded, JavaScript code remains unprocessed

Within a mobile website, there is a JavaScript snippet that appears as follows:

<script type="text/javascript">
(function() {
  // actual function code is not shown here
}());
</script>

Upon initial page load, the code is successfully executed. However, if the user navigates back to the previous page and then returns to this page, the code fails to execute a second time. This behavior is only observed when the page is accessed using an older Android browser with the following User-Agent header:

Mozilla/5.0 (Linux; U; Android 2.2.1; en-gb; GT-S5570 Build/FROYO) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

In contrast, on a more recent Android device with the following User-Agent header:

Mozilla/5.0 (Linux; Android 4.2.1; Galaxy Nexus Build/JOP40D) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166 Mobile Safari/535.19

the code successfully executes every time the page is loaded. Is this a known issue specific to the older browser in use? As a side note, what is the distinction between the following code snippets:

(function() {
  // function body omitted
}());

and

function() {
  // function body omitted
}();

javascript android mobile scope

Answer 1

Answer №1

Looking to address the second question, it's common to see people using Function expressions in this manner:

(function () {...}())

There exist 2 (3) types of functions:

function declarations
function expressions
function statements

Function declarations cannot be directly invoked. However, functions resulting from an expression can be invoked.

A correctly written immediately invoked function expression would appear like this:

(function() {
  // function body omitted
})();

In this instance, the function is converted into an expression by enclosing it in parentheses and then invoking it.

Nevertheless, this also works:

(function() {
  // function body omitted
}());

This is because the grouping operator ( around the function automatically transforms it into a function expression (which can be invoked). As a result, the function can be invoked by adding () immediately after the function body.

However, the structure like this:

function() {
  // function body omitted
}();

Is not valid due to the absence of the grouping operator, which notifies the interpreter that it is an expression. Without this, it remains a function declaration that cannot be directly invoked.

For a detailed explanation on these 3 types, check out this informative Article.

Answer 2

Looking to address the second question, it's common to see people using Function expressions in this manner:

(function () {...}())

There exist 2 (3) types of functions:

function declarations
function expressions
function statements

Function declarations cannot be directly invoked. However, functions resulting from an expression can be invoked.

A correctly written immediately invoked function expression would appear like this:

(function() {
  // function body omitted
})();

In this instance, the function is converted into an expression by enclosing it in parentheses and then invoking it.

Nevertheless, this also works:

(function() {
  // function body omitted
}());

This is because the grouping operator ( around the function automatically transforms it into a function expression (which can be invoked). As a result, the function can be invoked by adding () immediately after the function body.

However, the structure like this:

function() {
  // function body omitted
}();

Is not valid due to the absence of the grouping operator, which notifies the interpreter that it is an expression. Without this, it remains a function declaration that cannot be directly invoked.

For a detailed explanation on these 3 types, check out this informative Article.

When the page is reloaded, JavaScript code remains unprocessed

Answer №1

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