I am trying to reconstruct the exact sequence of executed Javascript functions (call graph) from log data gathered using the Tracing Profiler, particularly from the category “v8.cpu_profiler”. Unfortunately, the number of nodes (function definitions) and edges (function calls) I obtain fluctuates …
Tag: v8
What is the meaning of the prefix ‘Speculative’ and ‘Checked’ of Turbofan operators?
In the Turbofan IR, there are several operators whose name begins with ‘Speculative’ or ‘Checked’ (e.g. SpeculativeSafeIntegerAdd, CheckedInt32Add, CheckedFloat64ToInt32, …). What is the meaning of those prefix? Answer “SpeculativeSafeIntegerAdd” means “type fee…
Would calling Performance API frequently be causing a performance issue?
I want to measure the memory usage of my web SPA using performance.memory, and the purpose is to detect if there is any problem i.e. memory leak during the webapp’s lifetime. For this reason I would need to call this API for specific time interval – it could be every 3 second, every 30 second, or …
In V8, what is lazy deoptimization, and how does it happen?
According to V8 source code and turbofan materials, there is a type of deoptimization called lazy deoptimization which is described as follows(v8/src/common/globals.h): Lazy: the code has been marked as dependent on some assumption which is checked elsewhere and can trigger deoptimization the next time the co…
Canvas API implementation
I recently started to learn a bit about how javascript work under the hood, and came to know that (in the context of chrome) v8 engine and web APIs are different. Here’s some questions I have regarding the canvas API specifically: Why do we need to use getImageData() every time we want to access the pix…
Concurrency optimization job in V8
When concurrency optimization is triggered, a new optimization job will be dispatched to a child-thread to complete. How does Runtime know that the optimization job has been completed? I’ve found that in runtime function StackGuard, the optimized code will be set in JSFunction, but I don’t know ho…
Three different `this` behaviours for three different JS engines
I was learning about the this keyword and how it means different things with regards to regular functions vs ES6 arrow functions and function expressions and I came across something odd when trying to run the following code in Chrome, Deno and Node. So I prepared following: Example: Deno output: Node output: …
Do get accessors incur a per-instance allocation cost?
Say I have a class defined like this: And then I create several instances like so: Are these get accessors allocated for each instance? That is, would the memory usage of each of those objects increase if I were to add more get accessors, or are the get accessors allocated once and simply shared amongst all t…
Hooking Function Constructor (JavaScript)
Does anyone know of a way to detect when a new function is created? I know you can hook the function class constructor but that will only detect new Function() calls, not function func(){} declarations. I assume the JS engine just creates a default function class when it sees a function declaration instead of…
Why does this dynamic programming optimization actually make code slower?
This is from Leetcode problem: Concatenated Words. Below is a working solution. I added what I thought to be an optimization (see code comment), but it actually slows down the code. If I remove the wrapping if statement, it runs faster. To me, the optimization helps avoid having to: call an expensive O(n) sub…