# Script Timing

When using Frida, **timing** is everything—because classes and methods might not be **loaded** or **instantiated** when your script runs. If you try to use `Java.choose()` or `Java.use()` too early, you’ll get errors like:

```jsx
ClassNotFoundException: Didn't find class ...
```

**Here’s how to control timing properly:**

### 🛠️ ***Frida's App Launch Modes***

| **Mode**          | **Description**                                                           |
| ----------------- | ------------------------------------------------------------------------- |
| `-U -f <package>` | **Spawns** the app (cold start). Script runs **before app fully loads**.  |
| `-U -n <package>` | **Attaches** to a running app. Script runs after the app is fully loaded. |
| `-U -p <pid>`     | Attaches to a process by PID (also used after app is already running).    |

* Use **`-n`** if you want to avoid timing issues and let the app load fully.

### ⏳**Delaying Execution with `setTimeout()`**

If you must use `-f` (spawn), add a delay so your code runs after the app initializes:

```jsx
Java.perform(function () {
    setTimeout(function () {
        // Hook logic here
    }, 2000); // 2-second delay
});
```

### 🔄 Hooking Lifecycle Methods for Precise Timing

Instead of guessing with `setTimeout()`, you can **hook a known method** like `onCreate()` of an activity:

```jsx
Java.perform(function () {
    var Activity = Java.use("com.mobilehackinglab.FridaSix.MainActivity");

    Activity.onCreate.overload("android.os.Bundle").implementation = function (bundle) {
        console.log("[+] onCreate called — app is ready");

        // Safe to do stuff here
        var checker = Java.use("com.mobilehackinglab.FridaSix.Checker");
        var checker_obj = checker.$new();
        checker_obj.x.value = 1337;
        checker_obj.y.value = 1200;

        this.getFlag(checker_obj);

        // Call original
        return this.onCreate(bundle);
    };
});

```

### **`Java.perform()` vs `Java.performNow()`**

| **Function**        | **Behavior**                                                       |
| ------------------- | ------------------------------------------------------------------ |
| `Java.perform()`    | Executes your code **after Java VM is ready**. Safe and preferred. |
| `Java.performNow()` | Executes **immediately**, assumes VM is ready (risky with `-f`).   |

* Use `Java.performNow()` **only if you're sure** the VM and classes are ready (e.g., with `-n` or from another hook).

***


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