Html form element attributes onchange

By: moto25 Date of post: 12.07.2017

HTML form elements work a little bit differently from other DOM elements in React, because form elements naturally keep some internal state. For example, this form in plain HTML accepts a single name:. This form has the default HTML form behavior of browsing to a new page when the user submits the form. If you want this behavior in React, it just works. But in most cases, it's convenient to have a JavaScript function that handles the submission of the form and has access to the data that the user entered into the form.

The standard way to achieve this is with a technique called "controlled components". In React, mutable state is typically kept in the state property of components, and only updated with setState.

We can combine the two by making the React state be the "single source of truth". Then the React component that renders a form also controls what happens in that form on subsequent user input. An input form element whose value is controlled by React in this way is called a "controlled component".

New HTML 5 Input Types and Attributes

For example, if we want to make the previous example log the name when it is submitted, we can write the form as a controlled component:.

Since the value attribute is set on our form element, the displayed value will always be this.

HTML onchange Event Attribute

Since handleChange runs on every keystroke to update the React state, the displayed value will update as the user types. With a controlled component, every state mutation will have an associated handler function. This makes it straightforward to modify or validate user input. For example, if we wanted to enforce that names are written with all uppercase letters, we could write handleChange as:.

For example, this HTML creates a drop-down list of flavors:. Note that the Coconut option is initially selected, because of the selected attribute. React, instead of using this selected attribute, uses a value attribute on the root select tag.

javascript - Onchange event for Html-form-elements in td tag with Chrome - Stack Overflow

This is more convenient in a controlled component because you only need to update it in one place. When you need to handle multiple controlled input elements, you can add a name attribute to each element and let the handler function choose what to do based on the value of event. Note how we used the ES6 computed property name syntax to update the state key corresponding to the given input name:. Also, since setState automatically merges a partial state into the current state , we only needed to call it with the changed parts.

It can sometimes be tedious to use controlled components, because you need to write an event handler for every way your data can change and pipe all of the input state through a React component. This can become particularly annoying when you are converting a preexisting codebase to React, or integrating a React application with a non-React library.

In these situations, you might want to check out uncontrolled components , an alternative technique for implementing input forms. React Docs Tutorial Community Blog GitHub v Edit on GitHub Forms.

html form element attributes onchange

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