Why Doesn't My `setState` Update Reflect Immediately in My React Component?

setState in React: Navigating Asynchronous Updates

Background:

In React, setState() is used to update the component's state. However, it's important to note that setState() is not always immediate. It may be executed asynchronously, leading to potential discrepancies in state values.

The Specific Issue:

A user facing an issue reports inconsistencies in state updates using setState() in a component method. Specifically, they observed that console.log statements accessing the state after setState() didn't always reflect the intended updated value.

Code Snippet:

let total = newDealersDeckTotal.reduce(function(a, b) {
  return a + b;
},
0);

console.log(total, 'tittal'); // outputs correct total

setTimeout(() => {
  this.setState({ dealersOverallTotal: total });
}, 10);

console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); // outputs incorrect total

Cause:

The issue arises due to the asynchronous nature of setState(). When the first console.log is executed, the state has not yet been updated. Therefore, it logs the incorrect value.

Solution:

To resolve this, it's recommended to use the callback function provided by setState() to access the updated state after the update has completed.

this.setState({ dealersOverallTotal: total }, () => {
  console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
}); 

In this revised code snippet, the second console.log is nested within the callback function. This ensures that it's executed only after the state has been updated, providing the correct value.

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