Awake vs Start execution order in Unity - Trade-offs & Expert Analysis

Overview - Awake vs Start execution order

What is it?

In Unity, Awake and Start are special methods called during a script's lifecycle. Awake runs first when the object is created or loaded, setting up essential data. Start runs later, just before the first frame update, and is used for initialization that depends on other objects being ready. Both help organize when and how your game objects prepare themselves.

Why it matters

Without knowing the difference and order of Awake and Start, your game objects might try to use data or other objects before they are ready, causing bugs or crashes. This can make your game unstable or behave unpredictably. Understanding their order helps you write reliable, clean code that runs smoothly every time.

Where it fits

Before learning Awake and Start, you should understand basic Unity scripting and the concept of game objects and components. After mastering this, you can learn about other lifecycle methods like Update, FixedUpdate, and OnEnable to control behavior over time.

Mental Model

Core Idea

Awake runs first to set up the object itself, then Start runs to prepare the object once everything else is ready.

Think of it like...

Imagine waking up in the morning: first you open your eyes (Awake) to get ready, then you get out of bed and start your day (Start) once the house is awake too.

┌───────────────┐
│ Scene Loads   │
└──────┬────────┘
       │
  ┌────▼─────┐
  │ Awake()  │  ← Runs first, sets up own data
  └────┬─────┘
       │
  ┌────▼─────┐
  │ Start()  │  ← Runs after Awake, when all objects are ready
  └──────────┘
       │
  ┌────▼─────┐
  │ Update() │  ← Runs every frame
  └──────────┘

Build-Up - 7 Steps

1

Foundation

Understanding Unity Script Lifecycle

Concept: Unity calls special methods on scripts at specific times to control behavior.

Unity scripts have built-in methods like Awake, Start, and Update. Awake is called when the script instance is loaded. Start is called before the first frame update if the script is enabled. Update runs every frame. These methods help organize code to run at the right time.

Result

You know that Awake, Start, and Update are special methods Unity calls automatically in a certain order.

Understanding the script lifecycle is the foundation for controlling when your code runs in Unity.

2

Foundation

What Awake Does in Unity

Concept: Awake is used to initialize variables or states before the game starts running.

Awake runs once when the object is created or loaded, even if the script is disabled. It is used to set up references or initialize data that does not depend on other objects being ready.

Result

Your object has its own data ready immediately after Awake runs.

Knowing Awake runs early helps you prepare your object’s internal state safely.

3

Intermediate

What Start Does and When It Runs

🤔Before reading on: Do you think Start runs before or after Awake? Commit to your answer.

Concept: Start runs after Awake and only if the script is enabled, used for initialization that depends on other objects.

Start is called once before the first frame update, but only if the script is enabled. It is useful for setup that requires other objects to be initialized, like accessing components on other game objects.

Result

Your object can safely interact with other objects because Start runs after all Awake calls.

Understanding Start’s timing prevents errors from accessing uninitialized objects.

4

Intermediate

Execution Order Between Multiple Objects

🤔Before reading on: If two objects have Awake and Start, which Awake runs first? Which Start runs first? Predict.

Concept: All Awake methods run before any Start methods, but the order of Awake between objects is not guaranteed.

Unity calls Awake on all objects first, in no guaranteed order, then calls Start on all enabled objects. This means you cannot rely on Awake order between objects but can rely on all Awake finishing before any Start begins.

Result

You know that Awake sets up all objects first, then Start initializes them with knowledge that all Awake calls are done.

Knowing this order helps you avoid bugs from assuming a specific Awake order between objects.

5

Intermediate

Using Awake and Start Together Safely

Concept: Use Awake for internal setup and Start for external setup that depends on other objects.

Write code in Awake to initialize your own data and references. Use Start to access or communicate with other objects, because by then all Awake calls have completed. This separation keeps your code safe and predictable.

Result

Your game objects initialize correctly without null references or timing bugs.

Separating setup responsibilities between Awake and Start reduces common initialization errors.

6

Advanced

Handling Script Enable/Disable with Awake and Start

🤔Before reading on: Does Awake run again if you disable and re-enable a script? What about Start? Commit your answer.

Concept: Awake runs only once when the object is created; Start runs once when the script is enabled the first time.

Awake is called once per object lifetime, even if the script is disabled and re-enabled. Start runs once when the script is enabled for the first time. Disabling and enabling a script does not cause Awake to run again, and Start will not run again either.

Result

You understand that Awake is for one-time setup and Start is for first-time enabled setup.

Knowing this prevents confusion about initialization when toggling script states.

7

Expert

Surprising Behavior with Script Execution Order Settings

🤔Before reading on: Can you control the order Awake and Start run across scripts? How? Commit your guess.

Concept: Unity allows setting script execution order to control Awake and Start order between scripts, but it only affects Start and Update, not Awake.

In Unity’s Project Settings, you can set script execution order to specify which scripts run Start and Update first. However, Awake always runs before Start and its order is not affected by this setting. This can cause subtle bugs if you expect Awake order control.

Result

You know how to control Start order but must be careful with Awake order assumptions.

Understanding script execution order settings helps avoid hard-to-find bugs in complex projects.

Under the Hood

Unity loads all game objects and their components, then calls Awake on each script instance to initialize internal data. After all Awake calls finish, Unity calls Start on enabled scripts to allow initialization that depends on other objects. This two-phase initialization ensures objects are ready before interaction. Internally, Unity manages these calls in its engine loop, guaranteeing Awake runs once per object creation and Start runs once per enabled script before the first frame.

Why designed this way?

Unity separates Awake and Start to solve the problem of initialization order and dependencies. Awake sets up the object itself without assumptions about others, while Start waits until all objects are awake, allowing safe cross-object references. This design avoids race conditions and null reference errors common in game development.

┌─────────────────────────────┐
│ Unity Engine Initialization │
└─────────────┬───────────────┘
              │
      ┌───────▼────────┐
      │ Load GameObjects│
      └───────┬────────┘
              │
      ┌───────▼────────┐
      │ Call Awake()    │  ← All Awake calls run here
      └───────┬────────┘
              │
      ┌───────▼────────┐
      │ Call Start()    │  ← All Start calls run here
      └───────┬────────┘
              │
      ┌───────▼────────┐
      │ Begin Update()  │  ← Frame updates start
      └────────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Does Awake run every time a script is enabled? Commit yes or no.

Common Belief: Awake runs every time the script is enabled or disabled.

Reality: Awake runs only once when the object is created or loaded, not on enable/disable.

Why it matters: Misunderstanding this causes repeated initialization code to run incorrectly, leading to bugs or performance issues.

Quick: Is the order of Awake calls between different objects guaranteed? Commit yes or no.

Common Belief: Awake runs in a predictable order between all objects.

Reality: The order of Awake calls between different objects is not guaranteed by Unity.

Why it matters: Assuming order can cause bugs when one object depends on another’s Awake having run first.

Quick: Does setting script execution order affect Awake call order? Commit yes or no.

Common Belief: Script execution order settings control Awake call order.

Reality: Script execution order settings affect Start and Update order, but not Awake order.

Why it matters: Expecting Awake order control can cause subtle bugs in initialization dependencies.

Quick: Can you safely access other objects in Awake? Commit yes or no.

Common Belief: You can always access other objects safely in Awake.

Reality: Other objects may not be initialized yet in Awake, so accessing them can cause errors.

Why it matters: Accessing uninitialized objects in Awake leads to null references and crashes.

Expert Zone

1

Awake runs even if the script component is disabled, but Start only runs if enabled, which can affect initialization logic.

2

Static variables initialized in Awake persist across scene loads if marked as DontDestroyOnLoad, affecting game state management.

3

Using coroutines in Start allows delayed initialization after all Awake calls, enabling complex setup sequences.

When NOT to use

Avoid relying on Awake for initialization that depends on other objects; use Start or custom initialization methods instead. For complex dependency graphs, consider using Unity’s ScriptableObjects or dependency injection frameworks.

Production Patterns

In large projects, developers use Awake to cache references and Start to register events or communicate with other systems. Script execution order settings are used to control Start order for critical systems like input or game managers. Coroutines in Start help stagger heavy initialization to avoid frame drops.

Connections

Initialization Order in Operating Systems

Both manage the order of starting components to avoid dependency issues.

Understanding how OS services start in order helps grasp why Unity separates Awake and Start to manage dependencies safely.

Object-Oriented Constructor vs Post-Constructor Initialization

Awake is like a constructor setting up the object, Start is like a post-constructor method that runs after all objects are created.

Knowing this helps understand why some initialization must wait until all objects exist.

Project Management Phases

Awake is like planning phase (setting up own tasks), Start is like execution phase (coordinating with others).

This connection shows how separating setup phases prevents chaos and ensures smooth collaboration.

Common Pitfalls

#1 Trying to access other objects in Awake assuming they are ready.

Wrong approach:

void Awake() {
otherObject.DoSomething(); // otherObject might not be initialized yet
}

Correct approach:

void Start() {
otherObject.DoSomething(); // safe because all Awake calls are done
}

Root cause:

Misunderstanding that Awake runs before other objects are fully initialized.

#2 Putting heavy initialization code in Start causing frame delays.

Wrong approach:

void Start() {
LoadLargeData(); // blocks frame
}

Correct approach:

void Start() {
StartCoroutine(LoadLargeDataAsync()); // spreads load over frames
}

Root cause:

Not using coroutines to avoid blocking the main thread during initialization.

#3 Assuming Awake runs again after disabling and enabling a script.

Wrong approach:

void OnEnable() {
Awake(); // manually calling Awake is wrong
}

Correct approach:

void OnEnable() {
// initialization code here if needed
}

Root cause:

Confusing Unity lifecycle methods and trying to force Awake to rerun.

Key Takeaways

Awake runs once when the object is created, setting up internal data regardless of script enabled state.

Start runs once before the first frame update, only if the script is enabled, and is used for initialization that depends on other objects.

All Awake calls run before any Start calls, but the order of Awake between objects is not guaranteed.

Script execution order settings control Start and Update order but do not affect Awake order.

Separating initialization between Awake and Start prevents bugs from uninitialized references and ensures reliable game behavior.