Instead, if a component needs to use a local state, assign the initial state to this.state directly in the constructor. constructor()ĭo not call setState() in constructor(). In this case, avoid using setState() here. It returns the same result each time it’s invoked, and it does not directly interact with the browser. The render() function should be pure, meaning that it does not modify a component’s state. Let’s look at a few methods and how they react when calling setState() render()Ĭalling setState() here makes it possible for a component to produce infinite loops. There are a few methods where calling setState() leads to undesirable results and others to avoid completely. Using setState() in React lifecycle methodsĬalling setState() in React’s lifecycle methods requires a certain level of caution. SetState() always leads to a rerender unless shouldComponentUpdate() returns false. returns 0 because even though the value is set with setState(), it was only scheduled and not rerendered before attempting to use the value with this.state. This is why trying to use this.state immediately after a setState() leads to incorrect behaviors: // Trying to change the value of from previous example UNPKG IMPORT SETSTATE FROM REACT UPDATESetState() can be considered as a request instead of an immediate command to update the component. This boosts performance by avoiding unnecessary rerenders. React intentionally waits until all components call setState() in their event handlers before rerendering. The setState() schedule changes to the component’s state object and tells React that the component and its children must rerender with the updated state: // Correct Use the setState() method everywhere else doing so accepts an object that eventually merges into the component’s existing state.įor example, the following does not rerender a component: // Wrong The only place you should directly write to this.state is the component’s constructor method. This is done through the constructor method: import React, How do I update my component state in React?Īlthough it is technically possible to write to this.state from anywhere in your code, it does not prompt a rerender, which would lead to unstable and incorrect state values when trying to access values through this.state. UNPKG IMPORT SETSTATE FROM REACT CODEIn the code block below, we are setting the component’s initial state. Using setState() in React lifecycle methodsĬomponents that have a state are referred to as stateful components, while those that do not have states are stateless components.Ī component can have an initial state set, access it, and update it.How do I update my component state in React?.How do I access a component state in React?.User actions, network activity, API requests, or specific application behaviors can often trigger changes in state for React components. Unlike props, states are managed completely within the component and can be changed over time. States in React, like props, are objects that store data and affect how a component renders or behaves. It may still contain information that is out of date. tState(function(previousState, currentProps), console.Nosa Obaseki Follow Front-end dev currently building amazing products □□□ Using setState in React componentsĮditor’s note: This post was last updated on 30 July 2021. of previous state before updating any values. This is most often used when you want to check or make use Using setState() with a Function as updater // Set initial state (ONLY ALLOWED IN CONSTRUCTOR) Also demonstrates where the state can be set directly and where setState should be used. An example ES6 style component, updating the state on a simple button click. Using setState() with an Object as updater // The setState method accepts an updater argument that can either be an object with a number of key-value-pairs that should be merged into the state, or a function that returns such an object computed from prevState and props. Due to the fact that calls to setState() are not guaranteed by React to be atomic, this can sometimes be useful if you want to perform some action after you are positive that setState() has been executed successfully.
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