To merge an array of strings into a single string split by a new line in PHP, you can use the `implode` function to join the array elements into a single string, with the new line character (`\n`) as the delimiter.

Here's an example code snippet:

// An array of strings
$array_of_strings = array('Hello', 'world', 'in', 'PHP');

// Merge the array into a single string with new line delimiter
$merged_string = implode("\n", $array_of_strings);

// Output the merged string
echo $merged_string;

Output:

To check if a string starts with a number in Node.js, you can use a regular expression. 

Here's an example code snippet that checks if a string starts with a number:

const myString = "5abc";
const startsWithNumber = /^\d/.test(myString);

console.log(startsWithNumber); // true

In the code above, we first define a string `myString` that starts with the number 5. We then create a regular expression `/^\d/` that matches any string that starts with a digit (`\d`). 

To remove string duplicates from an array in Node.js, you can use the `filter` method along with the `indexOf` method.

Here's an example: