11.Stock-based compensation

The Company measures stock-based compensation expense on the grant date, based on the fair value of the award, and recognizes the expense on a straight-line basis over the requisite service period for awards expected to vest. The Company estimated the grant date fair value of stock options using a Black-Scholes valuation model using the following weighted-average assumptions for the periods indicated:

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The Company granted 97 and 163 stock options during the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. The stock-based compensation expense charged against operating income for stock options was $2,204 and $2,134 for the 13 weeks ended November 2, 2019 and November 3, 2018, respectively. The stock-based compensation expense charged against operating income for stock options was $6,523 and $6,557 for the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. The weighted-average grant date fair value of these stock options was $89.91 and $50.10 for the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. At November 2, 2019, there was approximately $18,105 of unrecognized stock-based compensation expense related to unvested stock options.

The Company issued 52 and 95 restricted stock units during the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. The stock-based compensation expense charged against operating income for restricted stock units was $3,429 and $3,449 for the 13 weeks ended November 2, 2019 and November 3, 2018, respectively. The stock-based compensation expense charged against operating income for restricted stock units was $9,672 and $9,244 for the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. At November 2, 2019, there was approximately $24,383 of unrecognized stock-based compensation expense related to restricted stock units.

The Company issued 21 and 33 performance-based restricted stock units during the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. The stock-based compensation benefit included in operating income for performance-based restricted stock units was $122 for the 13 weeks ended November 2, 2019. The stock-based compensation expense charged against operating income for performance-based restricted stock units was $1,904 for the 13 weeks ended November 3, 2018. The stock-based compensation expense charged against operating income for performance-based restricted stock units was $2,979 and $5,083 for the 39 weeks ended November 2, 2019 and November 3, 2018, respectively. At November 2, 2019, there was approximately $7,793 of unrecognized stock-based compensation expense related to performance-based restricted stock units.