Split Temporary Variable

Problem

One local variable is reused for several unrelated values: first a count, later a percentage, later a label. Each reader has to track which meaning is live at which line, and extracting any fragment drags the shared variable along.

Solution

Declare a separate, well-named const for each purpose. Loop accumulators (sum += x) and collecting variables are the exception: they hold one meaning that grows.

Before

function summarizeFunnel(events: AnalyticsEvent[]): string {
  let temp = events.filter((e) => e.type === "visit").length;
  const visits = temp;

  temp = events.filter((e) => e.type === "signup").length;
  const signupRate = visits === 0 ? 0 : temp / visits;

  temp = events.filter((e) => e.type === "purchase").length;
  const purchaseRate = visits === 0 ? 0 : temp / visits;

  return `visits=${visits} signup=${(signupRate * 100).toFixed(1)}% purchase=${(purchaseRate * 100).toFixed(1)}%`;
}

After

function summarizeFunnel(events: AnalyticsEvent[]): string {
  const visits = events.filter((e) => e.type === "visit").length;
  const signups = events.filter((e) => e.type === "signup").length;
  const purchases = events.filter((e) => e.type === "purchase").length;

  const signupRate = visits === 0 ? 0 : signups / visits;
  const purchaseRate = visits === 0 ? 0 : purchases / visits;

  return `visits=${visits} signup=${(signupRate * 100).toFixed(1)}% purchase=${(purchaseRate * 100).toFixed(1)}%`;
}

Why

• Each name states one meaning for its whole lifetime.
• const lets the compiler reject accidental reassignment.
• Fragments become independent, so Extract Method and Replace Temp with Query apply cleanly.

Steps

1. Find the first assignment of the reused variable. Rename the variable at that assignment and its reads up to the next assignment. Declare it const.
2. Compile and run the tests.
3. At the next assignment, declare a new const with a name for that purpose and update the reads that follow it.
4. Repeat until each assignment has its own variable. Delete the original declaration if nothing uses it.

Watch out

• Don't split accumulators or loop counters whose reassignments all serve one meaning (total += line.amount).
• Check closures. A callback created earlier may capture the original variable and observe later values; splitting changes what it sees.
• If the variable is a function parameter, apply Remove Assignments to Parameters instead.
• There is no useful inverse. Merging unrelated values into one variable is the smell itself.

Related

• Helps with Long Method.
• Prepares for Replace Temp with Query and Extract Method.
• Remove Assignments to Parameters is the same fix for parameters.

Agent checklist

• Every reassignment served a different purpose; accumulators were left alone.
• Each new variable is const and named for its meaning.
• No closure captured the old variable and relied on later values.
• Tests pass.