PHP Developer Interview Questions

Responsibilities

PHP developer responsibilities may include:

• Designing application phases
• Developing and designing PHP code
• Developing technical designs for applications and software
• Providing troubleshooting services as needed
• Testing code across various devices to ensure quality across all platforms
• Maintaining product software and databases

Skills

PHP is a popular server-side general programming language. In order to utilize this code to provide a pleasant user experience, skilled PHP developers will:

• Possess an understanding of open-source projects
• Possess experience in third-party API’s
• Communicate clearly with their team
• Use customer feedback to improve product quality
• Stay on top of industry trends

Qualifications

Many entry-level positions will prefer applicants with a bachelor’s degree in computer science or a related field. For candidates seeking a managerial position, a master’s degree in computer science or a related field is required.

However, candidates without formal education can still find employment as a freelancer if they have relevant experience and demonstrate an expert understanding of the code. There are many online certification programs and boot camps candidates can enroll in to make themselves more appealing.

If you’re getting ready to interview for a position as a PHP developer, you can prepare by researching the company as much as possible. Learn about the 9 things you should research before an interview.

Salary

Salaries for PHP developers range between $52K and $83K with the median being $66K. 

Factors impacting the salary you receive as a PHP developer include:

• Degrees (associate's or equivalent technical certifications, bachelor's, master's)
• Years of Experience
• Location
• Reporting Structure (seniority of the manager you report to and number of direct reports)
• Level of Performance - exceeding expectations

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PHP Developer Interview Questions

Question: How do you allow for error reporting when programming in PHP?

Explanation: The interviewer is opening the interview with an operational question. The purpose of an operational question is to determine how you go about doing your job. It provides the interviewer with some background about your qualifications for this position. Operational questions should be answered directly and briefly. The interviewer will ask a follow-up question if they need additional information.

Example: “To enable error reporting while programming in PHP, you would first check if display_errors is equal to on in the php.ini file. You can also add ini_set('display_errors', 1) in your script. Once you’ve completed this, you  include error_reporting(E_ALL) in your code to display all types of error messages during the script execution.”

Question: Once you have enabled error reporting, what are the main error types in PHP, and what are the differences between them?

Explanation: This is a follow-up question to the previous one. Since you mentioned all types of error messages in your last answer, the interviewer has chosen to explore this in more detail. You should always be prepared for follow-up questions when you provide an answer during an interview.

Example: “There are three different types of error messages within PHP. These include:

• Notices which are non-critical errors that occur during the execution of the script

• Warnings which are more critical errors than notices but still allow scripts to continue to execute

• Fatal which will terminate the execution of a script when it occurs.”

Question: Can you discuss traits and describe their function within PHP?

Explanation: The interviewer is asking you a technical question. You can recognize technical questions by their format. They first ask you to define a term and then describe how it is used within the job title for which you are interviewing. Technical questions are also best answered directly and succinctly. Like operational questions, you should anticipate follow-up questions once you have provided an answer.

Example: “Traits are mechanisms used to create reusable code within PHP. Traits are common to multiple programming languages. Within PHP, a trait cannot be instantiated. Also, multiple inheritances are not supported.”

Question: While a script is functioning, can the value of one of the constants change?

Explanation: This is another operational question. It requires you to have knowledge of scripts and some of their features. While this is a simple yes or no question, it will help you demonstrate your knowledge and experience as a PHP developer.

Example: “No. Once the value of a constant is declared during the execution of a PHP script, it cannot be changed.”

Question: Can the final defined class be extended?

Explanation: This is another yes or no question which tests your knowledge of PHP programming. During an interview, you can expect a variety of different questions, including general, operational, behavioral, and technical. The interviewer will switch between them periodically. They may also ask similar questions multiple times to calibrate your answers and determine if they are consistent.

Example: “No, a final defined class cannot be extended. One of the features of a final class or method declaration is preventing child class or method overriding.”

Question: What are the construct and destruct methods used in a PHP class?

Explanation: The interviewer is asking this question to understand your knowledge about the basics of OOP within PHP programming. The question is technical in nature because it is asking you to define these two terms.  Along with your definitions, you should provide a brief description of how these functions are used when programming in PHP.

Example: “Every object within PHP has construct and destruct methods built in. The construct method is used when a new instance of a class is created, and it is used to initialize class properties. The destruct method takes no parameters.”

Question: How do you determine the number of elements in a PHP array?

Explanation: This is another operational question asking how you go about doing your job.  By now, you should be comfortable answering both operational and technical questions.

Example: “The count function is used to determine and report the number of elements in a PHP array. This is known as a helper function because it doesn’t execute an operation other than providing information to the developer.”

Question: What is the syntax for creating a command which declares a function that receives one parameter name of hello?

Explanation: This is a hybrid operational and technical question. In addition to asking how you go about performing this task, it also asks you to define a specific term. As the interview progresses, you should anticipate the questions will become more specific and more difficult. This indicates the interviewer is gaining confidence in your ability and is willing to explore more complex topics.

Example: “The syntax I would use for creating a command which declares a function with a single parameter named hello is as follows: ‘If hello is true, then print hello; if function doesn’t receive hello or hello is false, print bye.’ This demonstrates that a parameter can or cannot be on the function call.” 

Question: How would you define the three scope levels available in PHP?

Explanation: You probably already recognized this as an operational question. The interviewer is looking to confirm your understanding of privileges and the accessibility of code. Understanding scope levels helps protect the integrity of data in your application and provides a clear path through the code. Your answer should demonstrate this.

Example: "The three levels of scope are private in which the data is only visible in its own class, public which enables the data to be visible to any other code accessing the class, and protected which only allows classes parent(s) and classes that extend the current class to access the data."

Question: Within the context of PHP, what are getters and setters, and how do you use them?

Explanation: This is another operational question. The terms the interviewer is asking about are typically only found in more advanced environments. Because of their unique applications within PHP, they are not well known. Being able to answer this question indicates you have advanced PHP development skills and will demonstrate your qualifications for the job.

Example: “Getters and setters are methods used to declare or obtain values of variables. They are important because they allow for a function to access data before declaring it or returning it to the developer. These functions can handle data that will be passed into a variable or other functions.”

Additional PHP Developer Interview Questions

• How would you get the IP address of a client?

• What are SQL Injections, and how do you prevent them?

• Have you ever led a team? What was the outcome of the team project?

• How much work have you done with database design and/or maintenance?

• What’s the difference between unset() and unlink()?