Svelte Tutorial - 10 - List Rendering
Summary
TLDRThis video script teaches how to display lists in web applications using Svelte's 'each' block. It demonstrates iterating over arrays of strings and objects to render HTML elements dynamically. The script covers basic syntax, using aliases for current items, and optionally displaying indices. It also touches on iterating over arrays of objects, accessing properties like first and last names, and hints at the next topic: using keys for lists in Svelte.
Takeaways
- đ Building web applications often requires displaying lists of items, such as names, products, or courses.
- đ In Svelte, the 'each' block is used to repeat HTML for each item in a list.
- đ The syntax for an 'each' block involves using curly braces, a hash symbol, and the block name, followed by an alias for the current item.
- đĄ To display a list of names, define an array in the script section and use the 'each' block to iterate over it, binding each name to the HTML.
- đ The 'each' block syntax includes an alias for the current item and optionally the index, which can be used for additional context.
- đ When rendering a list, the 'each' block will iterate as many times as there are items in the array, binding the current item to the HTML each time.
- đ If inspecting the rendered HTML, you'll see the element repeated for each item in the array, with the inner text reflecting the current item.
- đą For lists with an index, the index is provided by Svelte and can be displayed alongside the item.
- đ· Iterating over an array of objects is similar, but you access properties like 'first' and 'last' names using dot notation on the alias.
- đ The 'each' block can also include a 'key' expression for more efficient re-rendering of lists with dynamic content.
Q & A
What is the purpose of using the 'each' block in Svelte?
-The 'each' block in Svelte is used to iterate over a list of items, such as an array, and repeat a block of HTML for each item in the list.
How do you define an array of strings in Svelte's script section?
-You define an array of strings in Svelte's script section by using the `const` keyword followed by the array name and its values enclosed in square brackets, e.g., `const names = ['Bruce', 'Clark', 'Diana'];`.
What is the syntax for starting an 'each' block in Svelte?
-The syntax for starting an 'each' block in Svelte is `{#each arrayName as alias}` where `arrayName` is the name of the array you want to iterate over and `alias` is the variable to refer to the current item in the loop.
How do you end an 'each' block in Svelte?
-An 'each' block in Svelte is ended with `{/each}` followed by the name of the block if necessary.
What does the 'as' keyword do in the 'each' block syntax?
-The 'as' keyword in the 'each' block syntax is used to create an alias for the current item in the array during each iteration of the loop.
How can you display the items of an array in the UI using Svelte?
-You can display the items of an array in the UI by binding the alias to the HTML elements within the 'each' block, allowing the same HTML structure to be repeated for each item.
Can you access the index of the current item in an 'each' block iteration?
-Yes, in Svelte, you can access the index of the current item by using the syntax `{#each arrayName as item, index}`.
What happens if you want to iterate over an array of objects in Svelte?
-When iterating over an array of objects, you can access the properties of each object using the alias and the property names, e.g., `{#each fullNames as name (index)}` where `name.first` and `name.last` can be used to access the first name and last name properties.
How can you display the index of items in an 'each' block iteration?
-You can display the index of items in an 'each' block iteration by binding the index to an HTML element within the 'each' block, e.g., `{#each names as name (index)}` and then using `{index + 1}` to display the index starting from 1.
What is the key expression in the 'each' block, and what is its purpose?
-The key expression in the 'each' block is used to provide a unique identifier for each item in the array, which helps Svelte efficiently update the DOM when the list changes. It is mentioned as a topic for the next video in the script.
Outlines
đ Using the 'each' Block in Svelt for Lists
This paragraph explains how to use the 'each' block in Svelt to render lists of items. It begins with a general introduction to the common need for displaying lists in web applications and then provides a step-by-step guide on how to implement the 'each' block. The example given involves creating a constant 'names' which is an array of strings, and the goal is to display this list in the UI. The 'each' block syntax is introduced, including how to iterate over the 'names' array with 'names as name', and how to bind the current item to HTML using curly braces. The paragraph also touches on how to display the index of the current item in the list and how to iterate over an array of objects, accessing both the first and last names.
đ Understanding the Key Expression in Svelt's 'each' Block
Building upon the previous paragraph, this section delves into the advanced usage of the 'each' block, specifically mentioning the key expression which can be provided for an 'each' block. The paragraph starts by summarizing the understanding of the 'each' block and its application in rendering lists of elements. It then introduces the concept of the key expression, which is a missing piece for a complete understanding of the 'each' block functionality. Although the key expression is not explained in detail within this paragraph, it sets the stage for further exploration in the subsequent video, promising to provide more insights into keys and lists in Svelt.
Mindmap
Keywords
đĄWeb Applications
đĄList
đĄSvelte
đĄeach block
đĄHTML
đĄUI
đĄArray
đĄAlias
đĄIndex
đĄObject
đĄKey Expression
Highlights
Building web applications often requires displaying lists of items such as names, products, or courses.
In Svelte, the 'each' block is used to repeat HTML for each item in a list.
The 'each' block syntax is introduced with a hash symbol and the keyword 'each', followed by the data and alias.
An example demonstrates using the 'each' block with an array of strings for names.
The 'each' block iterates over the array, binding each item to the HTML.
Each iteration of the 'each' block creates a new instance of the bound HTML element.
The index of the current item can be accessed within the 'each' block for additional rendering needs.
An example shows rendering the index alongside names for a list.
Iterating over an array of objects is also possible with the 'each' block.
Objects in the array can be aliased and their properties accessed using dot notation.
A demonstration of rendering a list of full names with first and last names from an array of objects.
The 'each' block can also render additional information like index numbers for lists.
Svelte's reactivity ensures that changes in the data array are reflected in the UI.
The 'each' block is a powerful feature for creating dynamic lists in Svelte applications.
Understanding the 'each' block is crucial for effective list rendering in Svelte.
The next video will cover the 'key' expression for the 'each' block, enhancing list rendering.
Transcripts
when you build web applications
a common scenario is to display a list
of items
for example a list of names a list of
products
a list of courses and so on
so what we want is to repeat some html
for each item in the list in swelt
we can achieve that using the each block
let's understand the syntax with an
example
in the script section i'm going to
define a constant
called names which is an array of three
strings
bruce clarke and
diana our aim is to
display this list of names in the ui
for which we need to use the each block
if you can recollect from the previous
video you know that we use
curly braces to represent a block in the
markup
so within the main tag i'm going to add
a pair of curly braces
we represent the starting of a block
with the hash
symbol and this block is the each block
we end this block with curly braces a
forward slash
and the name of the block again
now we need a way to get hold of each
name
in the names array and the syntax for
that
is names as
name and this is swelt specific syntax
so let's understand what is happening
here
in each block names is the data
defined in the script section and name
is simply an alias to refer to the
current item
in the loop since we have three names
the each block basically iterates three
times
with name referring to each of the names
this name is what we bind to the html
using
curly braces so within the each block
add an hsu tag we are going to bind
text name
so first iteration name is equal to the
string
bruce second iteration name is equal to
clark
and third iteration name is equal to
diana
if we save the file and take a look at
the browser
we see the names being displayed
if you inspect element you can see that
the h2 tag
is repeated three times and the inner
text
is bruce clark and diana
so the h2 element has repeated itself
for each
name in the names array
sometimes you might also want to get
hold of the index
when rendering a list for that swelt
provides the index
in the each block which you can use if
required
so instead of just name we get hold
of name comma index
then while binding we can also bind
the index
index plus one
if we take a look at the browser we can
see
one two three next to the names
index starts at zero and hence index
plus
1 will represent 1 2 and 3.
now a small variation of this is
iterating over
an array of objects let's quickly take a
look at an example
going to create a new constant called
full names and this is going to be equal
to
an array of objects
so we have first name and last name
bruce wayne clark kent and princess
diana
now the aim is to display the list of
full names
in the ui if you have understood the
first example
this should be fairly straightforward to
understand
within the main tag at the top i'm going
to add
another each block so hashtag
or hash symbol followed by the keyword
each we also need to close
the each block using the forward slash
now for the iteration we are iterating
over
full names and we are going to alias
each object as name
we can also get hold of the index
within the each block i'm going to add
an h2 tag
and we can render index plus one
but this time while rendering the first
and last names
we need to access name dot first
and name dot last
name here refers to each object in the
iteration
if we now save the file and head back to
the browser
we should be able to see bruce wayne
clark kent
and princess diana and of course the
numbers are also displayed
all right you should now have a good
understanding of
the each block and its usage to render a
list of
elements in swell but there is still a
missing piece
which is the key expression that can be
provided
for an each block let's understand
more about keys and lists in the next
video
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