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Questions and Answers
When should you prefer directly manipulating the style property of an element using JavaScript instead of using CSS classes?
When should you prefer directly manipulating the style property of an element using JavaScript instead of using CSS classes?
- When calculating styles dynamically at runtime. (correct)
- When applying styles that are static and predefined.
- When the styles need to be applied based on a user's browser.
- When applying styles to multiple elements simultaneously.
Why was className introduced as a property in JavaScript, instead of directly using class?
Why was className introduced as a property in JavaScript, instead of directly using class?
- `className` is more performant than `class`.
- `class` was initially a reserved word in JavaScript. (correct)
- `className` allows for more complex class manipulations.
- `class` is only applicable in server-side JavaScript.
What is the primary difference between using elem.className and elem.classList when modifying CSS classes in JavaScript?
What is the primary difference between using elem.className and elem.classList when modifying CSS classes in JavaScript?
- `elem.className` replaces the entire string of classes, while `elem.classList` allows manipulation of individual classes. (correct)
- `elem.className` only works in older browsers, while `elem.classList` is for modern browsers.
- `elem.className` is used for adding classes, while `elem.classList` is used for removing them.
- `elem.className` automatically applies transitions, while `elem.classList` does not.
Which classList method would you use to ensure a certain class is present on an element, adding it if it's missing and removing it if it's already there?
Which classList method would you use to ensure a certain class is present on an element, adding it if it's missing and removing it if it's already there?
How can you iterate over all the classes applied to an element using classList?
How can you iterate over all the classes applied to an element using classList?
What is the correct JavaScript syntax to set the background color of an element with the ID 'myElement' to blue?
What is the correct JavaScript syntax to set the background color of an element with the ID 'myElement' to blue?
Given an element with `style="z-index: 10; color: red;"
Given an element with `style="z-index: 10; color: red;"
If an element has the classes 'class1 class2 class3', what would element.className = '' do?
If an element has the classes 'class1 class2 class3', what would element.className = '' do?
Consider an element el with el.classList.add('a', 'b', 'c'). Which of the following is the most accurate behavior across modern browsers?
Consider an element el with el.classList.add('a', 'b', 'c'). Which of the following is the most accurate behavior across modern browsers?
Given an HTML element, which approach offers the most efficient way to add and remove multiple classes dynamically based on complex application state changes?
Given an HTML element, which approach offers the most efficient way to add and remove multiple classes dynamically based on complex application state changes?
Flashcards
CSS Classes
CSS Classes
The preferred method for styling elements, offering more flexibility and easier maintenance.
Inline Styles
Inline Styles
Directly writing style properties, suitable for dynamic calculations but less flexible than CSS classes.
className
className
A property that corresponds to the 'class' attribute of an element. Assigning to it replaces the entire string of classes.
classList
classList
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classList.add(class)
classList.add(class)
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classList.remove(class)
classList.remove(class)
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classList.toggle(class)
classList.toggle(class)
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classList.contains(class)
classList.contains(class)
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elem.style
elem.style
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Camel Case in elem.style
Camel Case in elem.style
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Study Notes
- Prefer CSS classes over direct style manipulation in JavaScript for styling elements.
- Use JavaScript's
styleproperty only for dynamic calculations that CSS classes cannot handle.
className and classList
elem.classNamecorresponds to the "class" attribute of an element.- Assigning a value to
elem.classNamereplaces the entire string of classes. elem.classListprovides methods to manipulate individual classes.
Methods of classList
elem.classList.add("class")adds a class to the element.elem.classList.remove("class")removes a class from the element.elem.classList.toggle("class")adds the class if it doesn't exist, otherwise removes it.elem.classList.contains("class")checks if the element has a given class and returnstrueorfalse.classListis iterable, allowing listing of all classes usingfor...of.
Element style
- The
elem.styleproperty represents the "style" attribute of an element. - Setting properties of
elem.styleis equivalent to setting them directly in thestyleattribute. - Use camelCase for multi-word CSS properties when using
elem.style
Multi-word property to camelCase conversion:
background-colorbecomeselem.style.backgroundColorz-indexbecomeselem.style.zIndexborder-left-widthbecomeselem.style.borderLeftWidth
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