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# Using Dynamic Attributes

Using dynamic attributes, you can set attributes on elements using the result of expressions.

## Expression Value

The most common use case is inside a `vdl-repeat` or `vdl-repeat-contents` loop where the value or index of the loop iteration is needed to populate an attribute in a VDL or HTML element.

    <div vdl-repeat="=s,i in scenarios"
         vdl-attr="={id: 'scenarioId'+s.id}">
    </div>

This example results in each `div` in the repeat loop gaining an id attribute based on combining the string `scenarioId` with the `id` of each scenario referenced in the loop, which is all scenarios on the shelf.

## String Value

A slightly different syntax exists for those occasions when you can provide the value of `vdl-attr` as a string.

    <vdl-row vdl-repeat-contents="=num, idx in ['a','b','c']">
        <vdl-column vdl-attr="size: idx+1">
            ...
        </vdl-column>
    </vdl-row>

This works in the same way but is slightly more concise.
Parent Topic Working with Advanced VDL

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