Block JavaScript optimizations on these sites

What it does

Allows you to set a list of site URL patterns that specify sites for which advanced JavaScript optimizations are disabled. Disabling JavaScript optimizations means that Microsoft Edge may render web content more slowly. For detailed information on valid URL patterns, see https://go.microsoft.com/fwlink/?linkid=2095322. Wildcards, *, are allowed. You can set policy exceptions for specific subdomains and entire sites. For example, a policy set only for subdomain.contoso.com applies to subdomain.contoso.com without affecting contoso.com. In some cases, when a subdomain can't be isolated from its parent site, it may inherit the policy set on the parent site. Exceptions also may not take effect for frames loaded in an existing tab until the site is opened in a new tab. On low-memory Android devices, site-specific exceptions may not be enforced. Instead, sites use the policy from 'DefaultJavaScriptOptimizerSetting' (Control use of JavaScript optimizers), if set, or default to the profile's JavaScript optimization setting. To enforce exceptions, Microsoft Edge may place sites or subdomains with settings that differ from the default in dedicated processes. This behavior can increase memory usage, especially on Android devices or when a wildcard pattern matches many subdomains, because each matching origin may be isolated separately. Isolated subdomains also can't use document.domain to access their parent site. Note: In version 138 and earlier, policy exceptions were enforced only at the site level (eTLD+1). A policy set only for subdomain.contoso.com didn't take effect, even for subdomain.contoso.com. The policy had to be set on contoso.com to apply to both contoso.com and subdomain.contoso.com. This policy applies on a frame-by-frame basis and isn't based only on the top-level origin URL. For example, if contoso.com is listed in the 'JavaScriptOptimizerBlockedForSites' (Block JavaScript optimizations on these sites) policy, but contoso.com loads a frame that contains fabrikam.com, contoso.com has JavaScript optimizations disabled. However, fabrikam.com uses the policy from 'DefaultJavaScriptOptimizerSetting', if set, or defaults to JavaScript optimizations enabled. Blocklist entries have higher priority than allowlist entries, and allowlist entries have higher priority than the configured default value. If you don't configure this policy for a site, the policy from 'DefaultJavaScriptOptimizerSetting' applies to the site, if set. Otherwise, JavaScript optimization is enabled for the site. Example value: [*.]example.edu

What it writes

Hive

HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER

Registry key

Software\Policies\Microsoft\Edge

Options

Configure and deploy

Choose a state and the option values; the output below is generated from the template for exactly that.

Windows Registry Editor Version 5.00

[-HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites]

$ErrorActionPreference = 'Stop'

function Set-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $PropertyType,
        [Parameter(Mandatory = $true)][object] $Value
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        New-Item -Path $Path -Force | Out-Null
    }

    New-ItemProperty -LiteralPath $Path -Name $Name -PropertyType $PropertyType -Value $Value -Force | Out-Null
}

function Remove-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (Test-Path -LiteralPath $Path) {
        Remove-ItemProperty -LiteralPath $Path -Name $Name -Force -ErrorAction SilentlyContinue
    }
}

function Clear-RegistryKeyValues {
    param(
        [Parameter(Mandatory = $true)][string] $Path
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return
    }

    foreach ($propertyName in (Get-Item -LiteralPath $Path).Property) {
        Remove-ItemProperty -LiteralPath $Path -Name $propertyName -Force -ErrorAction SilentlyContinue
    }
}

# Policy: Block JavaScript optimizations on these sites
# Name: JavaScriptOptimizerBlockedForSites
# Scope: Machine
# State: Enabled
# Source: msedge.admx

Clear-RegistryKeyValues -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites'

./Device/Vendor/MSFT/Policy/Config/ADMX_msedge/JavaScriptOptimizerBlockedForSites

$ErrorActionPreference = 'Stop'
$reasons = [System.Collections.Generic.List[string]]::new()

function Test-RegistryValueExists {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return $false
    }

    return $null -ne (Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction SilentlyContinue)
}

function Test-RegistryValueEquals {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $Kind,
        [Parameter(Mandatory = $true)][object] $Expected
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return $false
    }

    $valueObject = Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction SilentlyContinue
    if ($null -eq $valueObject) {
        return $false
    }

    $actual = $valueObject.$Name
    switch ($Kind) {
        'String' { return [string]$actual -ceq [string]$Expected }
        'ExpandString' { return [string]$actual -ceq [string]$Expected }
        'DWord' { return [uint32]$actual -eq [uint32]$Expected }
        'QWord' {
            $actualBits = if ($actual -is [uint64]) { $actual } else { [BitConverter]::ToUInt64([BitConverter]::GetBytes([int64]$actual), 0) }
            $expectedBits = if ($Expected -is [uint64]) { $Expected } else { [BitConverter]::ToUInt64([BitConverter]::GetBytes([int64]$Expected), 0) }
            return $actualBits -eq $expectedBits
        }
        'MultiString' {
            $actualArray = @($actual)
            $expectedArray = @($Expected)
            if ($actualArray.Count -ne $expectedArray.Count) { return $false }
            for ($index = 0; $index -lt $actualArray.Count; $index++) {
                if ([string]$actualArray[$index] -cne [string]$expectedArray[$index]) { return $false }
            }
            return $true
        }
        'Binary' {
            $actualArray = [byte[]]$actual
            $expectedArray = [byte[]]$Expected
            if ($actualArray.Length -ne $expectedArray.Length) { return $false }
            for ($index = 0; $index -lt $actualArray.Length; $index++) {
                if ($actualArray[$index] -ne $expectedArray[$index]) { return $false }
            }
            return $true
        }
        default { return [string]$actual -ceq [string]$Expected }
    }
}

# Policy: Block JavaScript optimizations on these sites
# Name: JavaScriptOptimizerBlockedForSites
# Scope: Machine
# State: Enabled
# Source: msedge.admx

$keyPath = 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites'
if (Test-Path -LiteralPath $keyPath) {
    $propertyNames = (Get-Item -LiteralPath $keyPath).Property
    if ($propertyNames.Count -gt 0) {
        $reasons.Add('Key should be empty: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites') | Out-Null
    }
}

if ($reasons.Count -eq 0) {
    Write-Output 'Compliant'
    exit 0
}

$reasons | ForEach-Object { Write-Output $_ }
exit 1

$ErrorActionPreference = 'Stop'

function Set-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $PropertyType,
        [Parameter(Mandatory = $true)][object] $Value
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        New-Item -Path $Path -Force | Out-Null
    }

    New-ItemProperty -LiteralPath $Path -Name $Name -PropertyType $PropertyType -Value $Value -Force | Out-Null
}

function Remove-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (Test-Path -LiteralPath $Path) {
        Remove-ItemProperty -LiteralPath $Path -Name $Name -Force -ErrorAction SilentlyContinue
    }
}

function Clear-RegistryKeyValues {
    param(
        [Parameter(Mandatory = $true)][string] $Path
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return
    }

    foreach ($propertyName in (Get-Item -LiteralPath $Path).Property) {
        Remove-ItemProperty -LiteralPath $Path -Name $propertyName -Force -ErrorAction SilentlyContinue
    }
}

# Policy: Block JavaScript optimizations on these sites
# Name: JavaScriptOptimizerBlockedForSites
# Scope: Machine
# State: Enabled
# Source: msedge.admx

Clear-RegistryKeyValues -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites'

History 47 retained releases

1. 157.0.4341.425 Nov 2026
   Registry key: Software\Policies\Microsoft\Edge · Value name: Not specified
   • Description Allows you to set a list of site [removed: url][added: URL] patterns that specify sites for which advanced J…[removed: url][added: URL] patterns, see https://go.microsoft.com/fwlink/?linkid=2095…[removed: JavaScript optimization][added: You can set] policy exceptions [removed: will][added: for specific subdomains and entire sites. For example, a policy set] only [added: for subdomain.contoso.com applies to subdomain.contoso.com without affecting contoso.com. In some cases, when a subdomain can't ]be …
     Whole description, marked

     Allows you to set a list of site [removed: url][added: URL] patterns that specify sites for which advanced JavaScript optimizations are disabled. Disabling JavaScript optimizations means that Microsoft Edge may render web content more slowly. For detailed information on valid [removed: url][added: URL] patterns, see https://go.microsoft.com/fwlink/?linkid=2095322. Wildcards, *, are allowed. [removed: JavaScript optimization][added: You can set] policy exceptions [removed: will][added: for specific subdomains and entire sites. For example, a policy set] only [added: for subdomain.contoso.com applies to subdomain.contoso.com without affecting contoso.com. In some cases, when a subdomain can't ]be [removed: enforced at a site granularity (eTLD+1). A][added: isolated from its parent site, it may inherit the] policy set [added: on the parent site. Exceptions also may not take effect ]for [removed: only subdomain.contoso.com won't correctly apply][added: frames loaded in an existing tab until the site is opened in a new tab. On low-memory Android devices, site-specific exceptions may not be enforced. Instead, sites use the policy from 'DefaultJavaScriptOptimizerSetting' (Control use of JavaScript optimizers), if set, or default] to [removed: contoso.com][added: the profile's JavaScript optimization setting. To enforce exceptions, Microsoft Edge may place sites or subdomains with settings that differ from the default in dedicated processes. This behavior can increase memory usage, especially on Android devices] or [removed: subdomain.contoso.com since they both resolve][added: when a wildcard pattern matches many subdomains, because each matching origin may be isolated separately. Isolated subdomains also can't use document.domain] to [added: access their parent site. Note: In version 138 and earlier, policy exceptions were enforced only at ]the [removed: same eTLD+1 (contoso.com)][added: site level (eTLD+1). A policy set only] for [removed: which there's no policy. In this case,][added: subdomain.contoso.com didn't take effect, even for subdomain.contoso.com. The] policy [removed: must][added: had to] be set on contoso.com to apply [removed: correctly for ][added: to ]both contoso.com and subdomain.contoso.com. This policy applies on a frame-by-frame basis and isn't based [added: only ]on [added: the ]top-level origin [removed: url alone; so, for ][added: URL. For ]example, if contoso.com is listed in the 'JavaScriptOptimizerBlockedForSites' (Block JavaScript optimizations on these sites) [removed: policy][added: policy,] but contoso.com loads a frame [removed: containing][added: that contains] fabrikam.com, [removed: then ]contoso.com has JavaScript optimizations [removed: disabled, but][added: disabled. However,] fabrikam.com [removed: will use ][added: uses ]the policy from [removed: 'DefaultJavaScriptOptimizerSetting' (Control use of JavaScript optimizers), ][added: 'DefaultJavaScriptOptimizerSetting', ]if set, or [removed: default][added: defaults] to JavaScript optimizations enabled. Blocklist entries have higher priority than allowlist entries, [removed: which in turn][added: and allowlist entries] have higher priority than the configured default value. If you don't configure this policy for a site, [removed: then ]the policy from 'DefaultJavaScriptOptimizerSetting' applies to the site, if [removed: set; otherwise,][added: set. Otherwise,] JavaScript optimization is enabled for the site. Example value: [*.]example.edu

2. 150.0.4078.8016 Jul 2026
   • Already present in the first release ChangeIntel keeps.

45 later releases left it unchanged.

Template

Internal name

JavaScriptOptimizerBlockedForSites

Namespace

Microsoft.Policies.Edge

Template file

msedge.admx

Release

Microsoft Edge 157.0.4341.42 · file set 0c38d160a969619e…

<policy class="Both" displayName="$(string.JavaScriptOptimizerBlockedForSites)" explainText="$(string.JavaScriptOptimizerBlockedForSites_Explain)" key="Software\Policies\Microsoft\Edge" name="JavaScriptOptimizerBlockedForSites" presentation="$(presentation.JavaScriptOptimizerBlockedForSites)" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.Edge:ContentSettings" />
      <supportedOn ref="Microsoft.Policies.Edge:SUPPORTED_WIN7_V134" />
      <elements>
        <list id="JavaScriptOptimizerBlockedForSitesDesc" key="Software\Policies\Microsoft\Edge\JavaScriptOptimizerBlockedForSites" valuePrefix="" />
      </elements>
    </policy>

<presentation id="JavaScriptOptimizerBlockedForSites" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions"><listBox refId="JavaScriptOptimizerBlockedForSitesDesc">Block JavaScript optimizations on these sites</listBox></presentation>

Microsoft.Policies.Edge:category:ContentSettings
<category displayName="$(string.ContentSettings_group)" name="ContentSettings" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.Edge:microsoft_edge" />
    </category>
Microsoft.Policies.Edge:category:microsoft_edge
<category displayName="$(string.microsoft_edge)" name="microsoft_edge" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
Microsoft.Policies.Edge:definition:SUPPORTED_WIN7_V134
<definition displayName="$(string.SUPPORTED_WIN7_V134)" name="SUPPORTED_WIN7_V134" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
Microsoft.Policies.Edge:category:ContentSettings
<category displayName="$(string.ContentSettings_group)" name="ContentSettings" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.Edge:microsoft_edge" />
    </category>
<strings><string id="Microsoft.Policies.Edge:ContentSettings_group">Content settings</string></strings>
Microsoft.Policies.Edge:category:microsoft_edge
<category displayName="$(string.microsoft_edge)" name="microsoft_edge" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
<strings><string id="Microsoft.Policies.Edge:microsoft_edge">Microsoft Edge</string></strings>
Microsoft.Policies.Edge:definition:SUPPORTED_WIN7_V134
<definition displayName="$(string.SUPPORTED_WIN7_V134)" name="SUPPORTED_WIN7_V134" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
<strings><string id="Microsoft.Policies.Edge:SUPPORTED_WIN7_V134">Microsoft Edge version 134, Windows 7 or later</string></strings>