v => (console.log(v), v);

logIndent provides a logging function that does not interrupt your existing code. The function takes in a value, logs the value, then returns the value.

In addition to the standalone logIndent, this module provides a polyfill that adds logIndent to the global console object as console.ident.

I believe that logIndent should be a part of the standard, and as such I will be referring to it as console.ident going forward.

You can click here to jump to the API

You can view the slides and notes for my lighting talk proposing console.ident at Ident Presentation

Why

Javascript has become an Expression dominated language. Which means just about everything we do results in a value. Which in turn mean that we are able to write more concise code where one thing leads cleanly into the next.

For Example:

const userID = getUserId(
  JSON.parse(localStorage.getItem("user"))
);

const pickAndFormatData = ({ date, amount }) => ({
  date: moment(date).format("DD/MM/YYY "),
  amount: Number(amount) ? formatCurrency(amount) : amount
});

const result = arr
  .map(parseNumbers)
  .filter(removeOdds)
  .reduce(average);

But there is no console function that fit in modern style Javascript. Instead console.log and it's like return undefined. Which means you will have to awkwardly break up the code to debug it. console.ident solves the undefined issue. It takes in a value, logs the value, then returns the value.

For comparison:

With console.log:

const userStr = localStorage.getItem("user");
console.log(userStr);

const userID = getUserId(JSON.parse(userStr));

With console.ident:

const user = JSON.parse(
  console.ident(localStorage.getItem("user"))
);

With console.log:

const pickAndFormatData = ({ date, amount }) => {
  console.log(amount, Number(amount));
  
  const result = {
    date: moment(date).format("DD/MM/YYY "),
    amount: Number(amount) ? formatCurrency(amount) : amount
  };
  
  console.log(result);
  return result;
};

With console.ident:

const pickAndFormatData = ({ date, amount }) =>
  console.ident({
    date: moment(console.ident(date)).format("DD/MM/YYY"),
    amount: console.ident(Number(amount))
      ? formatCurrency(amount)
      : amount
  });

With console.log:

const filtered = arr.map(parseNumbers).filter(removeOdds);
console.log(filtered);

const result = filtered.reduce(average);

With console.ident:

const result = console.ident(arr
  .map(parseNumbers)
  .filter(removeOdds))
  .reduce(average);

API

logIdent( value, [options] )

Takes in a value, logs the value, then returns the value.

Developer consoles cannot accurately display the file name and line numbers for logIdent calls since they pull that information based on where where the console.log is called. To make up for that logIdent takes an optional second parameter that serves as an identifying label for the call.

Arguments

value (*): The value that will be logged and then returned.
[options] (*|IdentOptions):
      *: Any value that will be logged preceding the value as a label.
      IdentOptions (object):
            label (string): a value that will be logged preceding the value as a label.
            lineNumber (boolean): a flag to indicate if the function should add the line number where the function is being called from to the label

Example

import { logIdent } from "console.ident";

fetch(url)
  .then(res => res.json)
  .then(console.ident)
  .then(dispatchRecivedData);

import { logIdent } from "console.ident";

const filterOptionsByInputText = ({
  options,
  filterText
}) =>
  options.filter(value =>
    logIdent(value.contains(filterText), value)
  );

const SuggestionList = ({ options, filterText }) => (
  <ul>
    {options
      .filter(value =>
        logIdent(value.contains(filterText), {
          label: `${filterText} ${value}`,
          lineNumber: true
        })
      )
      .map(value => (
        <li key={value}>{value}</li>
      ))}
  </ul>
);

polyfill()

When called, this function will add logIdent to the global console object as console.ident

Example

import { polyfill } from "console.ident";
polyfill();

const value = console.ident("anything");